Ink composition, inkjet recording method, printed material, process for producing lithographic printing plate, and lithographic printing plate

ABSTRACT

An ink composition is provided that includes (A) an acid-generating compound having an anion represented by any one of Formulae (I) to (XI), (B) a cationically polymerizable compound, and (C) a colorant. 
     
       
         
         
             
             
         
       
     
     (In the formulae, R 1  to R 3  independently denote a monovalent organic group, Rb 1  to Rb 3 , Rf 1 , and Rf 2  independently denote a perfluoroalkyl group, a perfluoroaryl group, or an aryl group substituted with at least one fluorine atom or perfluoroalkyl group, X 1  to X 3  independently denote a monovalent organic group, and Y 1  denotes a hydrogen atom or a monovalent organic group.)

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an ink composition suitably used forinkjet recording, an inkjet recording method, and a printed materialemploying same; furthermore, it relates to a lithographic printing plateobtained using the ink composition, and a process for producing alithographic printing plate. More particularly, it relates to an inkcomposition suitable for inkjet recording that cures with highsensitivity upon exposure to radiation, can form a high quality image,and has good storage stability, an inkjet recording method, a printedmaterial employing same, a lithographic printing plate obtained usingthe ink composition, and a process for producing a lithographic printingplate.

2. Description of the Related Art

With regard to an image recording method for forming an image on arecording medium such as paper based on an image data signal, there arean electrophotographic system, sublimation type and melt type thermaltransfer systems, an inkjet system, etc. In the electrophotographicsystem, a process of forming an electrostatic latent image on aphotosensitive drum by electrically charging and exposing is required,and the system is complicated; as a result, there is the problem thatthe production cost is high. With regard to the thermal transfer system,although the equipment is inexpensive, due to the use of an ink ribbonthere is the problem that the running cost is high and waste material isgenerated. On the other hand, with regard to the inkjet system, theequipment is inexpensive and, since an image is formed directly on arecording medium by discharging an ink only on a required image area,the ink can be used efficiently and the running cost is low.Furthermore, there is little noise and it is excellent as an imagerecording system.

An ink composition that can be cured by exposure to radiation such asultraviolet rays and, in particular, an inkjet recording ink (radiationcuring type inkjet recording ink) are required to have sufficiently highsensitivity and provide a high image quality. By achieving highersensitivity, a large number of benefits are provided, such as highcurability toward radiation, a reduction in power consumption, longerlifetime due to a decrease in the load on a radiation generator, andprevention of formation of low molecular weight material originatingfrom insufficient curing. Furthermore, higher sensitivity particularlyimproves the cure strength of an image formed using the ink compositionand, in particular, the inkjet recording ink, particularly for theformation of a lithographic printing plate, and high plate life can beobtained.

As a cationic polymerization initiator, compounds disclosed byinventions described in, for example, JP-A-6-184170, JP-A-9-202873, andJP-A-9-221652 (JP-A denotes a Japanese unexamined patent applicationpublication) can be cited, and there is a desire for an ink compositionin which a cationically polymerizable compound has higher polymerizationefficiency and the ink composition has excellent sensitivity towardradiation.

BRIEF SUMMARY OF THE INVENTION

It is an object of the present invention, which has been accomplishedunder the above-mentioned circumstances, to provide an ink compositionthat cures with high sensitivity upon exposure to actinic radiation andhas excellent thermal stability, and an inkjet recording methodemploying the ink composition.

Furthermore, it is another object of the present invention to provide aprinted material and a lithographic printing plate obtained using an inkcomposition that can be cured with high sensitivity upon exposure toactinic radiation and has excellent thermal stability, and a process forproducing a lithographic printing plate.

The above-mentioned objects have been accomplished by (1), (6), or (8)to (10). They are described below together with (2) to (5), and (7),which are preferred embodiments.

(1) An ink composition comprising (A) an acid-generating compound havingan anion represented by any one of Formulae (I) to (XI), (B) acationically polymerizable compound, and (C) a colorant,

(in the formulae, R¹ to R³ independently denote a monovalent organicgroup, Rb¹ to Rb³, Rf¹, and Rf² independently denote a perfluoroalkylgroup, a perfluoroaryl group, or an aryl group substituted with at leastone fluorine atom or perfluoroalkyl group, X¹ to X³ independently denotea monovalent organic group, and Y¹ denotes a hydrogen atom or amonovalent organic group),(2) the ink composition according to (1) above, wherein theacid-generating compound has an anion represented by either Formula (I)or (II),(3) the ink composition according to (1) above, wherein theacid-generating compound has an anion represented by any one of Formulae(III) to (XI),(4) the ink composition according to (3) above, wherein theacid-generating compound has an anion represented by either Formula (VI)or (X),(5) the ink composition according to any one of (1) to (4) above,wherein it is for inkjet recording use,(6) an inkjet recording method comprising a step (A′) of discharging anink composition onto a recording medium, and a step (B′) of irradiatingthe discharged ink composition with actinic radiation so as to cure theink composition, the ink composition being the ink composition accordingto any one of (1) to (5) above,(7) the inkjet recording method according to (6) above, wherein theactinic radiation is ultraviolet radiation emitted by a light emittingdiode that has a light emission peak wavelength in the range of 350 to420 nm and generates ultraviolet radiation whose maximum illuminationintensity on the surface of a recording medium is 10 to 2,000 mW/cm²,(8) a printed material recorded by the inkjet recording method accordingto (6) or (7) above,(9) a process for producing a lithographic printing plate, the processcomprising a step (A″) of discharging the ink composition according toany one of (1) to (5) above onto a hydrophilic support, and a step (B″)of irradiating the discharged ink composition with actinic radiation soas to cure the ink composition, thus forming a hydrophobic image on thehydrophilic support by curing the ink composition, and(10) a lithographic printing plate produced by the process for producinga lithographic printing plate according to (9) above.

DETAILED DESCRIPTION OF THE INVENTION

The ink composition of the present invention (hereinafter, also simplycalled an ‘ink’) comprises (A) an acid-generating compound having ananion represented by any one of Formulae (I) to (XI) (hereinafter, alsosimply called an ‘acid-generating compound’), (B) a cationicallypolymerizable compound, and (C) a colorant.

(In the formulae, R¹ to R³ independently denote a monovalent organicgroup, Rb¹ to Rb³, Rf¹, and Rf² independently denote a perfluoroalkylgroup, a perfluoroaryl group, or an aryl group substituted with at leastone fluorine atom or perfluoroalkyl group, X¹ to X³ independently denotea monovalent organic group, and Y¹ denotes a hydrogen atom or amonovalent organic group.)

The acid-generating compound (A) having an anion represented by any oneof Formulae (I) to (XI) that can be used in the present invention ispreferable since it generates an acid having a very low pKa, high acidstrength, and high cationic polymerization initiation ability.Furthermore, the acid-generating compound (A) having an anionrepresented by any one of Formulae (I) to (XI) is preferable since itscounteranion species has very low nucleophilicity, a cationicpolymerization growth reaction is not inhibited, and high sensitivitycan be achieved. Moreover, it is preferable to use this counteranionspecies since the thermal decomposition temperature of the initiator isincreased and the stability over time can be improved. Furthermore, theacid-generating compound (A) having an anion represented by any one ofFormulae (I) to (XI) has a high solubility compared withhexafluorophosphoric acid, hexafluoroantimonic acid, etc., which areknown to give high cationic polymerizability.

The present invention is explained in detail below.

(1) Components Contained in Ink Composition

The ink composition of the present invention is radiation-curable,comprises (A) an acid-generating compound having an anion represented byany one of Formulae (I) to (XI) above, (B) a cationically polymerizablecompound, and (C) a colorant, and may comprise as necessary (D) asensitizer, (E) a co-sensitizer, (F) another polymerizable compound, (G)another polymerization initiator, and (H) another component.

The ‘radiation’ referred to in the present invention is not particularlylimited as long as it is actinic radiation that can provide energy thatenables an initiating species to be generated in the ink compositionwhen irradiated, and broadly includes α rays, γ rays, X rays,ultraviolet rays, visible light, and an electron beam; among these,ultraviolet rays and an electron beam are preferable from the viewpointof curing sensitivity and the availability of equipment, and ultravioletrays are particularly preferable. The ink composition of the presentinvention is therefore preferably an ink composition that can be curedby exposure to ultraviolet rays as radiation.

Furthermore, the ‘acid-generating compound’ referred to in the presentinvention means a compound that can generate a cationic polymerizationinitiating species such as an acid or a cation by irradiation withradiation.

The ink composition of the present invention can not only give a highquality printed material by forming an image having high image qualityand excellent strength when used in normal printing, but can also beused suitably for production of a resist, a color filter, or an opticaldisk, and is useful as a stereolithographic material or a holographicmaterial.

Furthermore, by employing an inkjet recording method, since by curingwith high sensitivity an image area having high strength can be formeddirectly on a non-absorbing recording medium based on digital data, theink composition of the present invention can be used suitably forproduction of a lithographic printing plate, in particular, a large arealithographic printing plate equal to or larger than A2 size, and thelithographic printing plate thus obtained has excellent plate life.

(A) Acid-Generating Compound Having an Anion Represented by any One ofFormulae (I) to (XI)

Rb¹ to Rb³ in the anion represented by Formula (I) or (II) independentlydenote a perfluoroalkyl group, a perfluoroaryl group, or an aryl groupsubstituted with at least one fluorine atom or perfluoroalkyl group. Itis also possible for at least two of Rb¹ to Rb³ to be bonded to form aring.

The aryl group substituted with at least one fluorine atom orperfluoroalkyl group may be a group having at least one fluorine atom orperfluoroalkyl group on the aryl ring, and preferred examples thereofinclude a 3,5-bistrifluoromethylphenyl group and a 3,5-difluorophenylgroup.

Preferred examples of the group formed by at least two of Rb¹ to Rb³being bonded include a perfluoroalkylene group and a perfluoroarylenegroup; a perfluoroalkylene group having 2 to 4 carbons is morepreferable, and a perfluoropropylene group is yet more preferable.

Rb¹ to Rb³ are preferably a perfluoroalkyl group or a perfluoroarylgroup, more preferably a perfluoroalkyl group having 1 to 8 carbons, andyet more preferably a perfluoroalkyl group having 1 to 4 carbons.

R¹ to R³ in the anion represented by any one of Formulae (III) to (XI)independently denote a monovalent organic group. It is also possible forat least two of R¹ to R³ to be bonded to form a ring.

Examples of the monovalent organic group include an alkyl group having 1to 20 carbons, an alkenyl group having 2 to 20 carbons, an alkynyl grouphaving 2 to 20 carbons, an aryl group having 6 to 20 carbons, anarylalkyl group having 7 to 21 carbons, a cyclic hydrocarbon grouphaving 3 to 20 carbons, and a heterocyclic group having 4 to 20 carbons.

The alkyl group denoted by R¹ to R³ preferably has 1 to 18 carbons, andparticularly preferably 1 to 12 carbons, may be a straight chain, andmay have a substituent.

The alkenyl group denoted by R¹ to R³ preferably has 2 to 18 carbons,and particularly preferably 2 to 12 carbons, and may further have asubstituent.

The alkynyl group denoted by R¹ to R³ preferably has 2 to 18 carbons,and particularly preferably 2 to 12 carbons, and may further have asubstituent.

The aryl group denoted by R¹ to R³ preferably has 6 to 14 carbons, andparticularly preferably 6 to 10 carbons, and may further have asubstituent.

The arylalkyl group denoted by R¹ to R³ preferably has 7 to 15 carbons,and particularly preferably 7 to 11 carbons, and may further have asubstituent.

The cyclic hydrocarbon group denoted by R¹ to R³ is a cyclic hydrocarbongroup other than the above-mentioned aryl group, and preferably asubstituted or unsubstituted cyclic hydrocarbon group having 3 to 14carbons.

The heterocyclic group denoted by R¹ to R³ is preferably a substitutedor unsubstituted heterocyclic group having 3 to 13 carbons, and thehetero atom contained in the heterocyclic group is preferably a nitrogenatom, an oxygen atom, or a sulfur atom.

Examples of the substituent that the alkyl group, the alkenyl group, thealkynyl group, the aryl group, the arylalkyl group, the cyclichydrocarbon group, and the heterocyclic group denoted by R¹ to R³ mayhave include the substituent groups below.

(Substituent Groups)

A halogen atom (a chlorine atom, a bromine atom, an iodine atom), analkyl group, an alkenyl group, an alkynyl group, an aryl group, anarylalkyl group, an acyl group, an alkoxycarbonyl group, a cyclichydrocarbon group, a heterocyclic group, a hydroxy group, an alkoxygroup, an aryloxy group, an N,N-dialkylamino group, an N,N-diarylaminogroup, an N-alkyl-N-arylamino group, an alkylsulfoxy group, anarylsulfoxy group, an N-alkylacylamino group, an N-arylacylamino group,an alkoxycarbonylamino group, an aryloxycarbonylamino group, anN-alkyl-N-alkoxycarbonylamino group, an N-alkyl-N-aryloxycarbonylaminogroup, an N-aryl-N-alkoxycarbonylamino group, an N,N-dialkylcarbamoylgroup, an N-arylcarbamoyl group, an N,N-diarylcarbamoyl group, anN-alkyl-N-arylcarbamoyl group, an alkylsulfinyl group, an arylsulfinylgroup, an alkylsulfonyl group, an arylsulfonyl group, anN,N-dialkylsulfinamoyl group, an N,N-diarylsulfinamoyl group, anN-alkyl-N-arylsulfinamoyl group, an N,N-dialkylsulfamoyl group, anN,N-diarylsulfamoyl group, an N-alkyl-N-arylsulfamoyl group, adialkylphosphono group (—PO₃(alkyl)₂), a diarylphosphono group(—PO₃(aryl)₂), an alkylarylphosphono group (—PO₃(alkyl)(aryl)), adialkylphosphonooxy group (—OPO₃(alkyl)₂), a diarylphosphonooxy group(—OPO₃(aryl)₂), an alkylarylphosphonooxy group (—OPO₃(alkyl)(aryl)), acyano group, a nitro group, an alkenyl group, an alkynyl group, and anoxo group.

These substituents may be further substituted with these substituents,and they may be bonded to each other to form a ring if this is possible.

When a fluorine atom is contained as a substituent, the groupcorresponding to Rf¹ or Rf², which will be described later, is notincluded as R¹ to R³.

Rf¹ and Rf² in the anion represented by any one of Formulae (III) to(XI) independently denote a perfluoroalkyl group, a perfluoroaryl group,or an aryl group substituted with at least one fluorine atom orperfluoroalkyl group. It is also possible for Rf¹ and Rf² to be bondedto form a ring.

The aryl group substituted with at least one fluorine atom orperfluoroalkyl group may be a group having at least one fluorine atom orperfluoroalkyl group on the aryl ring, and preferred examples thereofinclude a 3,5-bistrifluoromethylphenyl group and a 3,5-difluorophenylgroup.

Preferred examples of the group formed by Rf¹ and Rf² being bondedinclude a perfluoroalkylene group and a perfluoroarylene group.

Rf¹ and Rf² are preferably a perfluoroalkyl group or a perfluoroarylgroup, more preferably a perfluoroalkyl group having 1 to 8 carbons, andyet more preferably a perfluoroalkyl group having 1 to 4 carbons.

X¹ to X³ in the anion represented by any one of Formulae (III) to (XI)independently denote a monovalent organic group. It is also possible forat least two of X¹ to X³ to be bonded to form a ring.

Examples of the monovalent organic group include an alkyl group having 1to 20 carbons, an alkenyl group having 2 to 20 carbons, an alkynyl grouphaving 2 to 20 carbons, an aryl group having 6 to 20 carbons, anarylalkyl group having 6 to 21 carbons, a cyclic hydrocarbon grouphaving 3 to 20 carbons, a heterocyclic group having 4 to 20 carbons, anacyl group having 2 to 20 carbons, an alkylsulfinyl group having 1 to 20carbons, an arylsulfinyl group having 6 to 20 carbons, and a cyanogroup.

The alkyl group denoted by X¹ to X³ preferably has 1 to 18 carbons, andparticularly preferably 1 to 12 carbons, may be a straight chain, andmay have a substituent.

The alkenyl group denoted by X¹ to X³ preferably has 2 to 18 carbons,and particularly preferably 2 to 12 carbons, and may further have asubstituent.

The alkynyl group denoted by X¹ to X³ preferably has 2 to 18 carbons,and particularly preferably 2 to 12 carbons, and may further have asubstituent.

The aryl group denoted by X¹ to X³ preferably has 6 to 14 carbons, andparticularly preferably 6 to 10 carbons, and may further have asubstituent.

The arylalkyl group denoted by X¹ to X³ preferably has 7 to 15 carbons,and particularly preferably 7 to 11 carbons, and may further have asubstituent.

The cyclic hydrocarbon group denoted by X¹ to X³ is a cyclic hydrocarbongroup other than the above-mentioned aryl group, and is preferably asubstituted or unsubstituted cyclic hydrocarbon group having 3 to 14carbons.

The heterocyclic group denoted by X¹ to X³ is preferably a substitutedor unsubstituted heterocyclic group having 3 to 13 carbons, and thehetero atom contained in the heterocyclic group is preferably a nitrogenatom, an oxygen atom, or a sulfur atom.

The acyl group denoted by X¹ to X³ preferably has 2 to 18 carbons, andparticularly preferably 2 to 12 carbons, and may further have asubstituent.

The alkylsulfinyl group denoted by X¹ to X³ preferably has 2 to 18carbons, and particularly preferably 2 to 12 carbons, and may furtherhave a substituent.

The arylsulfinyl group having 6 to 20 carbons denoted by X¹ to X³preferably has 6 to 18 carbons, and particularly preferably 7 to 12carbons, and may further have a substituent.

Examples of the substituent that the alkyl group, the alkenyl group, thealkynyl group, the aryl group, the arylalkyl group, the cyclichydrocarbon group, and the heterocyclic group denoted by X¹ to X³ mayhave include the substituent groups below.

(Substituent Groups)

A halogen atom (a fluorine atom, a chlorine atom, a bromine atom, aniodine atom), an alkyl group, an alkenyl group, an alkynyl group, anaryl group, an arylalkyl group, an acyl group, an alkoxycarbonyl group,a cyclic hydrocarbon group, a heterocyclic group, a hydroxy group, analkoxy group, an aryloxy group, an N,N-dialkylamino group, anN,N-diarylamino group, an N-alkyl-N-arylamino group, an alkylsulfoxygroup, an arylsulfoxy group, an N-alkylacylamino group, anN-arylacylamino group, an alkoxycarbonylamino group, anaryloxycarbonylamino group, an N-alkyl-N-alkoxycarbonylamino group, anN-alkyl-N-aryloxycarbonylamino group, an N-aryl-N-alkoxycarbonylaminogroup, an N,N-dialkylcarbamoyl group, an N-arylcarbamoyl group, anN,N-diarylcarbamoyl group, an N-alkyl-N-arylcarbamoyl group, analkylsulfinyl group, an arylsulfinyl group, an alkylsulfonyl group, anarylsulfonyl group, an N,N-dialkylsulfinamoyl group, anN,N-diarylsulfinamoyl group, an N-alkyl-N-arylsulfinamoyl group, anN,N-dialkylsulfamoyl group, an N,N-diarylsulfamoyl group, anN-alkyl-N-arylsulfamoyl group, a dialkylphosphono group (—PO₃(alkyl)₂),a diarylphosphono group (—PO₃(aryl)₂), an alkylarylphosphono group(—PO₃(alkyl)(aryl)), a dialkylphosphonooxy group (—OPO₃(alkyl)₂), adiarylphosphonooxy group (—OPO₃(aryl)₂), an alkylarylphosphonooxy group(—OPO₃(alkyl)(aryl)), a cyano group, a nitro group, an alkenyl group, analkynyl group, and an oxo group.

These substituents may be further substituted with these substituents,and they may be bonded to each other to form a ring if this is possible.

From the viewpoint of reduction of the nucleophilicity of the anion, X¹to X³ are preferably a perfluoroalkyl group having 1 to 8 carbons or asubstituted aryl group having 6 to 12 carbons substituted with at leastone electron-withdrawing group such as a halogen atom, a cyano group, anitro group, a perfluoroalkyl group, an alkylsulfonyl group, anarylsulfonyl group, an alkoxycarbonyl group, or an aryloxycarbonylgroup, and more preferably a perfluoroalkyl group having 1 to 8 carbonsor a perfluoroaryl group having 6 to 12 carbons.

Y¹ in the anion represented by Formula (X) denotes a hydrogen atom or amonovalent organic group, and is preferably a hydrogen atom, an alkylgroup, or an aryl group, and more preferably a hydrogen atom. Themonovalent organic group denoted by Y¹ has the same meaning as that ofthe monovalent organic group denoted by X¹ to X³, and preferred rangesare also the same. It is also possible for Y¹ to be bonded to X¹ and/orX² to form a ring.

Furthermore, from the viewpoint of the synthetic suitability of thecompound and reduction of the nucleophilicity of the anion, a compoundhaving an anion represented by Formula (III) or Formula (XI) ispreferable, a compound having an anion represented by Formula (IV) orFormula (VII) is more preferable, and among them it is most preferablefor X¹ to X³ to be a perfluoroalkyl group having 1 to 8 carbons or aperfluoroaryl group having 6 to 12 carbons from the viewpoint ofreduction of the nucleophilicity of the anion. Furthermore, it is mostpreferable for Y¹ to be a hydrogen atom from the viewpoint of syntheticsuitability of the compound and reduction of the nucleophilicity of theanion.

Moreover, from the viewpoint of reduction of the nucleophilicity of theanion, a compound having an anion represented by Formula (I), Formula(II), Formula (III), Formula (VI), or Formula (X) is preferable, and acompound having an anion represented by Formula (VI) or Formula (X) ismore preferable.

Preferred specific examples of the anion represented by Formula (I) areillustrated below.

Furthermore, preferred specific examples of the anion represented byFormula (II) are illustrated below.

Preferred specific examples of the anion represented by any one ofFormulae (III) to (XI) are illustrated below. In the present invention,the chemical formula is expressed in the form of a simplified structureformula, and a solid line without an explicit element or substituentgroup denotes a hydrocarbon group.

A cation that pairs with the anion represented by any one of Formulae(I) to (XI) may be an onium ion of a known onium salt or anorganometallic cation, and may be a monovalent cation or a polyvalentcation.

Examples of the onium ion include onium ions such as iodonium,sulfonium, phosphonium, diazonium, ammonium, pyridinium, quinolinium,acridinium, oxonium, selenonium, and arsonium, and among these, oniumions such as iodonium, sulfonium, phosphonium, diazonium, quinolinium,and acridinium are preferable.

Examples of the onium ion include cations such as onium ions of oniumsalts of group 15 to 17 elements described in JP-A-6-184170, etc.,diazonium ions of diazonium salts described in S. I. Schlesinger,Photogr. Sci. Eng., 18, 387 (1974), T. S. Bal et al., Polymer, 21, 423(1980), etc., ammonium ions of ammonium salts described in U.S. Pat.Nos. 4,069,055, 4,069,056, and Re 27,992, JP-A-3-140140, etc.,phosphonium ions of phosphonium salts described in D. C. Necker et al.,Macromolecules, 17, 2468 (1984), C. S. Wen et al., Tech, Proc. Conf.Rad. Curing ASIA, p. 478 Tokyo, October (1988), U.S. Pat. Nos. 4,069,055and 4,069,056, JP-A-9-202873, etc., iodonium ions of iodonium saltsdescribed in J. V. Crivello et al., Macromolecules, 10 (6), 1307 (1977),Chem. & Eng. News, November 28, p. 31 (1988), European Patent Nos.104,143, 339,049, and 410,201, JP-A-2-150848, JP-A-2-296514, etc.,sulfonium ions of sulfonium salts described in J. V. Crivello et al.,Polymer J. 17, 73 (1985), J. V. Crivello et al., J. Org. Chem., 43, 3055(1978), W. R. Watt et al., J. Polymer Sci., Polymer Chem. Ed., 22, 1789(1984), J. V. Crivello et al., Polymer Bull., 14, 279 (1985), J. V.Crivello et al., Macromolecules, 14(5), 1141 (1981), J. V. Crivello etal., J. Polymer Sci., Polymer Chem. Ed., 17, 2877 (1979), EuropeanPatent Nos. 370, 693, 161, 811, 410, 201, 339,049, 233, 567, 297, 443,and 297,442, U.S. Pat. Nos. 3,902,114, 4,933,377, 4,760,013, 4,734,444,and 2,833,827, German Patent Nos. 2,904,626, 3,604,580, and 3,604,581,JP-A-7-28237, JP-A-8-27102, etc., quinolinium ions of quinolinium saltsdescribed in JP-A-9-221652, etc. selenonium ions of selenonium saltsdescribed in J. V. Crivello et al., Macromolecules, 10 (6), 1307 (1977),J. V. Crivello et al., J. Polymer Sci., Polymer Chem. Ed., 17, 1047(1979), etc., and arsonium ions of arsonium salts described in C. S. Wenet al., Tech, Proc. Conf. Rad. Curing ASIA, p. 478 Tokyo, October(1988), etc., but should not be construed as being limited thereto.

Furthermore, preferred examples of the onium ion in the acid-generatingcompound (A) include cations having structures represented by Formulae(Ca-I) to (Ca-VI) below.

In Formulae (Ca-I) to (Ca-VI) above, R¹ to R³ independently denote anaryl group, R⁴ to R⁶ independently denote an alkyl group, an alkenylgroup, an alkynyl group, an aryl group, a cyclic hydrocarbon group, or aheterocyclic group, R⁷ to R¹¹ independently denote an alkyl group, analkenyl group, an alkynyl group, an aryl group, a cyclic hydrocarbongroup, a heterocyclic group, an alkoxy group, or an aryloxy group, andR¹² to R¹⁷ independently denote a hydrogen atom, a halogen atom, or amonovalent organic group.

The alkyl group denoted by R⁴ to R¹¹ preferably has 1 to 30 carbons,more preferably 1 to 20 carbons, and particularly preferably 1 to 8carbons, may be a straight chain, and may have a substituent.

The alkenyl group denoted by R⁴ to R¹¹ preferably has 2 to 30 carbons,more preferably 2 to 20 carbons, and particularly preferably 2 to 8carbons, and may further have a substituent.

The alkynyl group denoted by R⁴ to R¹¹ preferably has 2 to 30 carbons,more preferably 2 to 20 carbons, and particularly preferably 2 to 8carbons, and may further have a substituent.

The aryl group denoted by R¹ to R¹¹ preferably has 6 to 30 carbons, morepreferably 6 to 20 carbons, and particularly preferably 6 to 10 carbons,and may further have a substituent.

The cyclic hydrocarbon group denoted by R⁴ to R¹¹ preferably has 3 to 30carbons, more preferably 3 to 20 carbons, and particularly preferably 3to 10 carbons, and may further have a substituent.

The heterocyclic group denoted by R⁴ to R¹¹ preferably has 4 to 30carbons, more preferably 4 to 20 carbons, and particularly preferably 4to 10 carbons, and may further have a substituent. Furthermore, thehetero atom contained in the heterocyclic group is preferably a nitrogenatom, an oxygen atom, or a sulfur atom.

The alkoxy group denoted by R⁷ to R¹¹ preferably has 1 to 30 carbons,more preferably 1 to 20 carbons, and particularly preferably 1 to 8carbons. Furthermore, the alkoxy group may have a substituent describedbelow, and the alkyl moiety of the alkoxy group may be an alkenyl group,an alkynyl group, a cyclic hydrocarbon group, or a heterocyclic groupother than an aromatic group.

The aryloxy group denoted by R⁷ to R¹¹ preferably has 6 to 30 carbons,more preferably 6 to 20 carbons, and particularly preferably 6 to 10carbons. Furthermore, the aryloxy group may have a substituent describedbelow, and the aryl moiety of the aryloxy group may be an aromaticheterocyclic group.

In Formula (Ca-II), R² and R³ may be bonded to each other to form a ringif this is possible.

In Formula (Ca-III), two or more of R⁴ to R⁶ may be bonded to each otherto form a ring if this is possible.

In Formula (Ca-IV), two or more of R⁷ to R¹⁰ may be bonded to each otherto form a ring if this is possible.

In Formula (Ca-V), two or more of R¹¹ to R¹⁴ may be bonded to each otherto form a ring if this is possible.

In Formula (Ca-VI), two or more of R¹⁵ to R¹⁷ may be bonded to eachother to form a ring if this is possible.

With regard to the substituent that may be possessed by the alkyl group,the alkenyl group, the alkynyl group, the aryl group, the hydrocarbongroup, the heterocyclic group, the alkoxy group, or the aryloxy group, amonovalent non-metallic atomic group other than hydrogen is used, andpreferred examples thereof include a halogen atom (—F, —Br, —Cl, —I), ahydroxyl group, an alkyl group, an aryl group, an alkenyl group, analkynyl group, an alkoxy group, an aryloxy group, a mercapto group, analkylthio group, an arylthio group, an alkyldithio group, an aryldithiogroup, an amino group, an N-alkylamino group, an N,N-dialkylamino group,an N-arylamino group, an N,N-diarylamino group, an N-alkyl-N-arylaminogroup, an acyloxy group, a carbamoyloxy group, an N-alkylcarbamoyloxygroup, an N-arylcarbamoyloxy group, an N,N-dialkylcarbamoyloxy group, anN,N-diarylcarbamoyloxy group, an N-alkyl-N-arylcarbamoyloxy group, analkylsulfoxy group, an arylsulfoxy group, an acylthio group,

an acylamino group, an N-alkylacylamino group, an N-arylacylamino group,a ureido group, an N′-alkylureido group, an N,N′-dialkylureido group, anN′-arylureido group, an N,N′-diarylureido group, anN′-alkyl-N′-arylureido group, an N-alkylureido group, an N-arylureidogroup, an N′-alkyl-N-alkylureido group, an N′-alkyl-N-arylureido group,an N,N′-dialkyl-N-alkylureido group, an N′,N′-dialkyl-N-arylureidogroup, an N′-aryl-N-alkylureido group, an N′-aryl-N-arylureido group, anN′,N′-diaryl-N-alkylureido group, an N,N′-diaryl-N-arylureido group, anN′-alkyl-N′-aryl-N-alkylureido group, an N′-alkyl-N′-aryl-N-arylureidogroup, an alkoxycarbonylamino group, an aryloxycarbonylamino group, anN-alkyl-N-alkoxycarbonylamino group, an N-alkyl-N-aryloxycarbonylaminogroup, an N-aryl-N-alkoxycarbonylamino group, anN-aryl-N-aryloxycarbonylamino group,

a formyl group, an acyl group, a carboxyl group and conjugate base groupthereof (hereinafter, called a carboxylate), an alkoxycarbonyl group, anaryloxycarbonyl group, a carbamoyl group, an N-alkylcarbamoyl group, anN,N-dialkylcarbamoyl group, an N-arylcarbamoyl group, anN,N-diarylcarbamoyl group, an N-alkyl-N-arylcarbamoyl group, analkylsulfinyl group, an arylsulfinyl group, an alkylsulfonyl group, anarylsulfonyl group, a sulfo group (—SO₃H) and conjugate base groupthereof (hereinafter, called a sulfonate group), an alkoxysulfonylgroup, an aryloxysulfonyl group, a sulfinamoyl group, anN-alkylsulfinamoyl group, an N,N-dialkylsulfinamoyl group, anN-arylsulfinamoyl group, an N,N-diarylsulfinamoyl group, anN-alkyl-N-arylsulfinamoyl group, a sulfamoyl group, an N-alkylsulfamoylgroup, an N,N-dialkylsulfamoyl group, an N-arylsulfamoyl group, anN,N-diarylsulfamoyl group, an N-alkyl-N-arylsulfamoyl group, anN-acylsulfamoyl group and conjugate base group thereof, anN-alkylsulfonylsulfamoyl group (—SO₂NHSO₂(alkyl)) and conjugate basegroup thereof, an N-arylsulfonylsulfamoyl group (—SO₂NHSO₂(aryl)) andconjugate base group thereof, an N-alkylsulfonylcarbamoyl group(—CONHSO₂(alkyl)) and conjugate base group thereof, anN-arylsulfonylcarbamoyl group (—CONHSO₂(aryl)) and conjugate base groupthereof,

a silyl group, an alkoxysilyl group (—Si(O-alkyl)₃), an aryloxysilylgroup (—Si(O-aryl)₃), a hydroxysilyl group (—Si(OH)₃) and conjugate basegroup thereof, a phosphono group (—PO₃H₂) and conjugate base groupthereof (hereinafter, called a phosphonate group), a dialkylphosphonogroup (—PO₃(alkyl)₂), a diarylphosphono group (—PO₃(aryl)₂), analkylarylphosphono group (—PO₃(alkyl)(aryl)), a monoalkylphosphono group(—PO₃H(alkyl)) and conjugate base group thereof (hereinafter, called analkylphosphonate group), a monoarylphosphono group (—PO₃H(aryl)) andconjugate base group thereof (hereinafter, called an arylphosphonategroup), a phosphonooxy group (—OPO₃H₂) and conjugate base group thereof(hereinafter, called a phosphonatooxy group), a dialkylphosphonooxygroup (—OPO₃(alkyl)₂), a diarylphosphonooxy group (—OPO₃(aryl)₂), analkylarylphosphonooxy group (—OPO₃(alkyl)(aryl)), amonoalkylphosphonooxy group (—OPO₃H(alkyl)) and conjugate base groupthereof (hereinafter, called an alkylphosphonatooxy group), amonoarylphosphonooxy group (—OPO₃H(aryl)) and conjugate base groupthereof (hereinafter, called an arylphosphonatooxy group), a cyanogroup, and a nitro group. These substituents may be further substitutedwith the above-mentioned substituent, and may form a ring if this ispossible.

R¹² to R¹⁷ independently denote a hydrogen atom, a halogen atom, or amonovalent organic group.

Examples of the halogen atom denoted by R¹² to R¹⁷ include a fluorineatom, a chlorine atom, a bromine atom, and an iodine atom, and afluorine atom, a chlorine atom, or a bromine atom is preferable.

Examples of the monovalent organic group denoted by R¹² to R¹⁷ include ahydroxyl group, an alkyl group, an alkenyl group, an alkynyl group, anaryl group, a cyclic hydrocarbon group, a heterocyclic group, an alkoxygroup, an aryloxy group, an acyl group, an alkoxycarbonyl group, anacyloxy group, —SO₃—R^(a), —NR^(b)R^(c), a cyano group,—SiR^(d)R^(e)R^(f), —SOR^(g), —SO₂R^(g), and a nitro group; R^(a)denotes a hydrogen atom, an alkyl group, an alkenyl group, an alkynylgroup, an aryl group, an arylalkyl group, an alkali metal atom, orquaternary ammonium, R^(b), R^(c), and R^(g) independently denote analkyl group, an alkenyl group, an alkynyl group, an aryl group, a cyclichydrocarbon group, or a heterocyclic group, and R^(d) to R^(f)independently denote an alkyl group, an alkenyl group, an alkynyl group,an aryl group, a cyclic hydrocarbon group, a heterocyclic group, analkoxy group, or an aryloxy group.

The alkyl group, alkenyl group, alkynyl group, aryl group, cyclichydrocarbon group, heterocyclic group, alkoxy group, and aryloxy groupdenoted by R¹² to R¹⁷ have the same meanings as those denoted by R⁷ toR¹¹ above, and preferred ranges are also the same. Furthermore, thesegroups may have the above-mentioned substituent.

The acyl group and the alkoxycarbonyl group denoted by R¹² to R¹⁷preferably have 1 to 30 carbons in the carbon chain side, andparticularly preferably 1 to 12 carbons, may be a straight chain, andmay have the above-mentioned substituent.

The acyloxy group denoted by R¹² to R¹⁷ preferably has 1 to 30 carbons,and particularly preferably 1 to 12 carbons, may be a straight chain,and may have the above-mentioned substituent.

R^(a) in —SO₃—R^(a) denoted by R¹² to R¹⁷ is preferably a hydrogen atom,the above-mentioned alkyl group, which may have a substituent, theabove-mentioned aryl group, which may have a substituent, a lithiumatom, a sodium atom, or a potassium atom.

The above-mentioned alkyl group, alkenyl group, alkynyl group, arylgroup, cyclic hydrocarbon group, and heterocyclic group denoted by R^(b)and R^(c) in —NR^(b)R^(c) have the same meanings as those denoted by R⁷to R¹¹ above, and preferred ranges are also the same. Furthermore, thesegroups may have the above-mentioned substituent.

The alkyl group, alkenyl group, alkynyl group, aryl group, cyclichydrocarbon group, heterocyclic group, alkoxy group, and aryloxy groupdenoted by R^(d) to R^(f) in —SiR^(d)R^(e)R^(f) have the same meaningsas those denoted by R⁷ to R¹¹ above, and preferred ranges are also thesame. Furthermore, these groups may have the above-mentionedsubstituent.

The alkyl group, alkenyl group, alkynyl group, aryl group, cyclichydrocarbon group, and heterocyclic group denoted by R^(g) in —SOR^(g)or —SO₂R^(g) have the same meanings as those denoted by R⁷ to R¹¹ above,and preferred ranges are also the same. Furthermore, these groups mayhave the above-mentioned substituent.

Preferred specific examples of the onium ion in the acid-generatingcompound (A) include countercations having the structures denoted byCa-1 to Ca-45 below.

The organometallic cation of the acid-generating compound (A) is acation containing a transition metal atom and a substituted orunsubstituted aromatic compound having an arene- orcyclopentadienyl-based ligand; it is an organometallic complex cationsubstantially not containing any metal hydride or any metal alkylfunctional group selected from compounds described in U.S. Pat. No.4,985,340, and is represented by the formula below.

[(L¹)(L²)M]^(q+)

In the formula, M denotes Cr, Mo, W, Mn, Re, Fe, Ru, Os, Co, Rh, Ir, Pd,Pt, or Ni; preferably Cr, Mo, W, Mn, Fe, Ru, Co, Pd, or Ni; and mostpreferably Mn or Fe, L¹ denotes one or two cyclic polyunsaturatedligands, which may be identical or different, selected from the groupconsisting of substituted and unsubstituted cyclopentadienyl,cyclohexadienyl, cycloheptatrienyl, cycloheptatriene, cyclooctatetraene,a heterocyclic compound, an aromatic compound (selected from substitutedand unsubstituted arene compounds), a compound having 2 to 4 condensedrings, and a polymer constituent unit [e.g. a phenyl group such aspolystyrene, poly(styrene-co-butadiene), poly(styrene-co-methylmethacrylate), or poly(α-methylstyrene); a cyclopentadiene group such aspoly(vinylcyclopentadiene); a pyridine group such aspoly(vinylpyridine), etc.], each ligand being capable of donating 3 to 8electrons to the valence shell of M; L² may be absent, or denotes 1 to 3non-anionic ligands, which may be identical or different, that donate aneven number of electrons, selected from the group consisting of carbonoxide, a ketone, an olefin, an ether, nitrosonium, a phosphine, aphosphite, an arsenic or antimony-related derivative, an organonitrile,an amine, an alkyne, isonitrile, and dinitrogen, provided that the totalelectric charge donated to M generates a net residual positive charge qfor said complex. q is an integer of 1 or 2, and denotes the residualcharge of said complex cation.

With regard to a process for producing the acid-generating compoundhaving an organometallic cation, methods described in EPO No. 094,914,and U.S. Pat. Nos. 5,089,536, 4,868,288, and 5,073,476 can be cited asexamples. The organometallic cation that can be used in the presentinvention is generally not useful as a catalyst for Ziegler-Natta orcoordination polymerization of an olefin or an acetylene. This isbecause such polymerization needs a metal hydride or a metal-alkylfunctional group, which is not present in a catalyst salt or aninitiator salt useful in the present invention. Furthermore, theacid-generating compound having an organometallic cation that can beused in the present invention does not need a metal hydride or a metalalkyl cocatalyst, which is normally used in a Ziegler-Natta orcoordination catalyst for polymerization of an olefin or an acetylene.In contrast to the Ziegler-Natta catalyst, the acid-generating compoundhaving an organometallic cation that can be used in the presentinvention is generally stable and active under external conditions thatinclude normal levels of oxygen and water in the air.

Preferred specific examples of the organometallic cation includebis(η⁵-cyclopentadienyl)iron⁽¹⁺⁾,(η⁵-isopropylcyclopentadienyl)(η⁵-cyclopentadienyl)iron⁽¹⁺⁾,(η⁵-cyclopentadienyl)(η⁶-xylene)iron⁽¹⁺⁾,(η⁵-cyclopentadienyl)(η⁶-toluene)iron⁽¹⁺⁾,(η⁵-cyclopentadienyl)(η⁶-mesitylene)iron⁽¹⁺⁾,(η⁵-cyclopentadienyl)(η⁶-pyrene)iron⁽¹⁺⁾,(η⁵-cyclopentadienyl)(η⁶-naphthalene)iron⁽¹⁺⁾,(η⁵-cyclopentadienyl)(η⁶-dodecylphenyl)iron⁽¹⁺⁾, bis(η⁶-xylene)iron⁽²⁺⁾,bis(η⁶-mesitylene)iron⁽²⁺⁾, bis(η⁶-durene)iron⁽²⁺⁾,bis(η⁶-pentamethylbenzene)iron⁽²⁺⁾, and bis(η⁶-dodecylbenzene)iron⁽²⁺⁾.

The onium ion used in the present invention is preferably atriarylsulfonium salt from the viewpoint of sensitivity and thermalstability, is preferably a triarylsulfonium salt substituted with atleast one electron-withdrawing group such as a trifluoromethyl group, ahalogen atom, an ester group, a sulfoxide group, a cyano group, an amidegroup, a carboxyl group, or a carbonyl group from the viewpoint ofimprovement of sensitivity, and is more preferably a triarylsulfoniumsalt substituted with at least one of a fluoro group (—F), atrifluoromethyl group (—CF₃), a chloro group (—Cl), and a bromo group(—Br), yet more preferably a sulfonium salt in which each aryl skeletonis substituted with a halogen atom, and most preferably a sulfonium saltsubstituted with three chloro groups.

The ink composition of the present invention generates an acid having ananion represented by any one of Formulae (I) to (XI) with a very lowpKa, the composition having a high acid strength and therefore a highability to initiate cationic polymerization. Furthermore, since thenucleophilicity of the counteranion species is very low, a growthreaction of the cationic polymerization is not inhibited, thus givinghigh sensitivity. Moreover, employing this counteranion makes thethermal decomposition temperature of the initiator high and improves thestability over time. Furthermore, it has high solubility compared with aknown acid-generating agent such as an onium salt that generateshexafluorophosphoric acid or hexafluoroantimonic acid, which is known togive high cationic polymerizability.

An onium salt having an anion represented by any one of Formulae (I) to(XI) may be synthesized by salt exchange between a metal salt or anammonium salt of an anion represented by any one of Formula (I) to (XI)and an onium salt compound (a halide, an acetate, a tetrafluoroborate, asulfonate, a perchlorate, etc.).

The above-mentioned acid-generating compound having an anion representedby any one of Formulae (I) to (XI) is preferably a compound formed bycombining a cation (Ca-1 to 45 or specific examples of theorganometallic cation) and an anion that are described above as specificexamples, and is more preferably a compound illustrated below.

The onium ion used in the present invention is preferably atriarylsulfonium from the viewpoint of sensitivity and thermalstability, is preferably a triarylsulfonium salt substituted with atleast one electron-withdrawing group such as a trifluoromethyl group, ahalogen atom, an ester group, a sulfoxide group, a cyano group, an amidegroup, a carboxyl group, or a carbonyl group from the viewpoint ofimprovement of sensitivity, and more preferably a triarylsulfonium saltsubstituted with at least one of a trifluoromethyl group, a fluorogroup, a chloro group, and a bromo group. It is preferably atriarylsulfonium salt in which each aryl group is substituted with atleast one halogen atom, and most preferably a triarylsulfonium salt inwhich each aryl group is substituted with one chloro group.

The acid-generating compound having an anion represented by any one ofFormulae (I) to (XI) may be added to the ink composition at a proportionof 0.1 to 50 wt % relative to the ink composition, more preferably 0.5to 30 wt %, and particularly preferably 1 to 20 wt %. It is preferablefor the amount added to be in the above-mentioned range since thesensitivity is good and a non-image area is not stained during printing.Such an onium-based polymerization initiator may be used singly or in acombination of two or more types.

(B) Cationically Polymerizable Compound

The ink composition of the present invention comprises a cationicallypolymerizable compound.

The cationically polymerizable compound that can be used in the presentinvention is not particularly limited as long as it is a compound thatundergoes a polymerization reaction by virtue of a cationicpolymerization initiating species generated by a cationic polymerizationinitiator, which will be described later, and is cured, and variousknown types of cationically polymerizable monomers known as cationicallyphotopolymerizable monomers may be used. Examples of the cationicallypolymerizable monomer include, for example, epoxy compounds, vinyl ethercompounds, and oxetane compounds described in JP-A-6-9714,JP-A-2001-31892, JP-A-2001-40068, JP-A-2001-55507, JP-A-2001-310938,JP-A-2001-310937, JP-A-2001-220526, etc. As the cationicallypolymerizable compound, for example, a cationically polymerizable typephotocuring resin is known, and in recent years cationicallyphotopolymerizable type photocuring resins sensitized to a visible lightwavelength region of 400 nm or longer have been disclosed in, forexample, JP-A-6-43633 and JP-A-8-324137.

Examples of the epoxy compounds include aromatic epoxides, alicyclicepoxides, and aliphatic epoxides, and examples of the aromatic epoxideinclude di- or polyglycidyl ethers produced by a reaction betweenepichlorohydrin and a polyhydric phenol having at least one aromaticnucleus or an alkylene oxide adduct thereof; specific examples includedi- or polyglycidyl ethers of bisphenol A or an alkylene oxide adductthereof, di- or polyglycidyl ethers of hydrogenated bisphenol A or analkylene oxide adduct thereof, and novolac type epoxy resins. Examplesof the alkylene oxide above include ethylene oxide and propylene oxide.

Examples of the alicyclic epoxides include cyclohexene oxide- andcyclopentene oxide-containing compounds obtained by epoxidizing acompound having at least one cycloalkene ring such as a cyclohexene ringor a cyclopentene ring with an appropriate oxidizing agent such ashydrogen peroxide or a peracid.

Examples of the aliphatic epoxides include di- or polyglycidyl ethers ofan aliphatic polyhydric alcohol or an alkylene oxide adduct thereof, andrepresentative examples thereof include diglycidyl ethers of an alkyleneglycol such as the diglycidyl ether of ethylene glycol, the diglycidylether of propylene glycol, and the diglycidyl ether of 1,6-hexanediol,polyglycidyl ethers of a polyhydric alcohol such as the di- ortriglycidyl ether of glycerol or an alkylene oxide adduct thereof, anddiglycidyl ethers of a polyalkylene glycol such as the diglycidyl etherof polyethylene glycol or an alkylene oxide adduct thereof and thediglycidyl ether of polypropylene glycol or an alkylene oxide adductthereof. Examples of the alkylene oxide above include ethylene oxide andpropylene oxide.

Detailed examples of monofunctional and polyfunctional epoxy compoundsthat can be used in the present invention are now given.

Examples of monofunctional epoxy compounds used in the present inventioninclude phenyl glycidyl ether, p-tert-butylphenyl glycidyl ether, butylglycidyl ether, 2-ethylhexyl glycidyl ether, allyl glycidyl ether,1,2-butylene oxide, 1,3-butadiene monooxide, 1,2-epoxydodecane,epichlorohydrin, 1,2-epoxydecane, styrene oxide, cyclohexene oxide,3-methacryloyloxymethylcyclohexene oxide, 3-acryloyloxymethylcyclohexeneoxide, and 3-vinylcyclohexene oxide.

Furthermore, examples of polyfunctional epoxy compounds includebisphenol A diglycidyl ether, bisphenol F diglycidyl ether, bisphenol Sdiglycidyl ether, brominated bisphenol A diglycidyl ether, brominatedbisphenol F diglycidyl ether, brominated bisphenol S diglycidyl ether,epoxy novolac resins, hydrogenated bisphenol A diglycidyl ether,hydrogenated bisphenol F diglycidyl ether, hydrogenated bisphenol Sdiglycidyl ether,2-(3,4-epoxycyclohexyl-5,5-spiro-3,4-epoxy)cyclohexane-meta-dioxane,bis(3,4-epoxycyclohexylmethyl)adipate,bis(3,4-epoxy-6-methylcyclohexylmethyl)adipate,3,4-epoxy-6-methylcyclohexenyl3′,4′-epoxy-6′-methylcyclohexenecarboxylate,methylenebis(3,4-epoxycyclohexane), dicyclopentadiene diepoxide, thedi(3,4-epoxycyclohexylmethyl)ether of ethylene glycol, ethylenebis(3,4-epoxycyclohexanecarboxylate), dioctyl epoxyhexahydrophthalate,di-2-ethylhexyl epoxyhexahydrophthalate, 1,4-butanediol diglycidylether, 1,6-hexanediol diglycidyl ether, glycerol triglycidyl ether,trimethylolpropane triglycidyl ether, polyethylene glycol diglycidylether, polypropylene glycol diglycidyl ether, 1,13-tetradecadienedioxide, limonene dioxide, 1,2,7,8-diepoxyoctane, and1,2,5,6-diepoxycyclooctane.

Among these epoxy compounds, the aromatic epoxides and the alicyclicepoxides are preferable from the viewpoint of excellent curing speed,and the alicyclic epoxides are particularly preferable.

Examples of the vinyl ether compounds include di- or tri-vinyl ethercompounds such as ethylene glycol divinyl ether, diethylene glycoldivinyl ether, triethylene glycol divinyl ether, propylene glycoldivinyl ether, dipropylene glycol divinyl ether, butanediol divinylether, hexanediol divinyl ether, cyclohexanedimethanol divinyl ether,and trimethylolpropane trivinyl ether, and monovinyl ether compoundssuch as ethyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether,octadecyl vinyl ether, cyclohexyl vinyl ether, hydroxybutyl vinyl ether,2-ethylhexyl vinyl ether, cyclohexanedimethanol monovinyl ether,n-propyl vinyl ether, isopropyl vinyl ether, isopropenyl vinylether-O-propylene carbonate, dodecyl vinyl ether, and diethylene glycolmonovinyl ether.

Detailed examples of monofunctional vinyl ethers and polyfunctionalvinyl ethers are given below.

Specific examples of monofunctional vinyl ethers include methyl vinylether, ethyl vinyl ether, propyl vinyl ether, n-butyl vinyl ether,t-butyl vinyl ether, 2-ethylhexyl vinyl ether, n-nonyl vinyl ether,lauryl vinyl ether, cyclohexyl vinyl ether, cyclohexylmethyl vinylether, 4-methylcyclohexylmethyl vinyl ether, benzyl vinyl ether,dicyclopentenyl vinyl ether, 2-dicyclopentenoxyethyl vinyl ether,methoxyethyl vinyl ether, ethoxyethyl vinyl ether, butoxyethyl vinylether, methoxyethoxyethyl vinyl ether, ethoxyethoxyethyl vinyl ether,methoxypolyethylene glycol vinyl ether, tetrahydrofurfuryl vinyl ether,2-hydroxyethyl vinyl ether, 2-hydroxypropyl vinyl ether, 4-hydroxybutylvinyl ether, 4-hydroxymethylcyclohexylmethyl vinyl ether, diethyleneglycol monovinyl ether, polyethylene glycol vinyl ether, chloroethylvinyl ether, chlorobutyl vinyl ether, chloroethoxyethyl vinyl ether,phenylethyl vinyl ether, and phenoxypolyethylene glycol vinyl ether.

Furthermore, examples of polyfunctional vinyl ethers include divinylethers such as ethylene glycol divinyl ether, diethylene glycol divinylether, polyethylene glycol divinyl ether, propylene glycol divinylether, butylene glycol divinyl ether, hexanediol divinyl ether,bisphenol A alkylene oxide divinyl ether, and bisphenol F alkylene oxidedivinyl ether; and polyfunctional vinyl ethers such as trimethylolethanetrivinyl ether, trimethylolpropane trivinyl ether, ditrimethylolpropanetetravinyl ether, glycerol trivinyl ether, pentaerythritol tetravinylether, dipentaerythritol pentavinyl ether, dipentaerythritol hexavinylether, an ethylene oxide adduct of trimethylolpropane trivinyl ether, apropylene oxide adduct of trimethylolpropane trivinyl ether, an ethyleneoxide adduct of ditrimethylolpropane tetravinyl ether, a propylene oxideadduct of ditrimethylolpropane tetravinyl ether, an ethylene oxideadduct of pentaerythritol tetravinyl ether, a propylene oxide adduct ofpentaerythritol tetravinyl ether, an ethylene oxide adduct ofdipentaerythritol hexavinyl ether, and a propylene oxide adduct ofdipentaerythritol hexavinyl ether.

As the vinyl ether compound, the di- or tri-vinyl ether compounds arepreferable from the viewpoint of curability, adhesion to a recordingmedium, surface hardness of the image formed, etc., and the divinylether compounds are particularly preferable.

The oxetane compound in the present invention means a compound having atleast one oxetane ring, and may be selected freely from known oxetanecompounds such as those described in JP-A-2001-220526, JP-A-2001-310937,and JP-A-2003-341217.

As the compound having an oxetane ring that can be used in the inkcomposition of the present invention, a compound having 1 to 4 oxetanerings in the structure is preferable. In accordance with use of such acompound, it becomes easy to maintain the viscosity of the inkcomposition in a range that gives good handling properties and,furthermore, the cured ink can be given high adhesion to the recordingmedium, which is preferable.

Examples of compounds having 1 to 2 oxetane rings in the moleculeinclude compounds represented by Formulae (1) to (3) below.

R^(a1) denotes a hydrogen atom, an alkyl group having 1 to 6 carbons, afluoroalkyl group having 1 to 6 carbons, an allyl group, an aryl group,a furyl group, or a thienyl group. When there are two R^(a1) in themolecule, they may be identical to or different from each other.

Examples of the alkyl group include a methyl group, an ethyl group, apropyl group, and a butyl group, and preferred examples of thefluoroalkyl group include those obtained by substituting any of thehydrogen atoms of the above alkyl groups with a fluorine atom.

R^(a2) denotes a hydrogen atom, an alkyl group having 1 to 6 carbons, analkenyl group having 2 to 6 carbons, a group having an aromatic ring, analkylcarbonyl group having 2 to 6 carbons, an alkoxycarbonyl grouphaving 2 to 6 carbons, or an N-alkylcarbamoyl group having 2 to 6carbons. Examples of the alkyl group include a methyl group, an ethylgroup, a propyl group, and a butyl group, examples of the alkenyl groupinclude a 1-propenyl group, a 2-propenyl group, a 2-methyl-1-propenylgroup, a 2-methyl-2-propenyl group, a 1-butenyl group, a 2-butenylgroup, and a 3-butenyl group, and examples of the group having anaromatic ring include a phenyl group, a benzyl group, a fluorobenzylgroup, a methoxybenzyl group, and a phenoxyethyl group. Examples of thealkylcarbonyl group include an ethylcarbonyl group, a propylcarbonylgroup, and a butylcarbonyl group, examples of the alkoxycarbonyl groupinclude an ethoxycarbonyl group, a propoxycarbonyl group, and abutoxycarbonyl group, and examples of the N-alkylcarbamoyl group includean ethylcarbamoyl group, a propylcarbamoyl group, a butylcarbamoylgroup, and a pentylcarbamoyl group. Furthermore, it is possible for R²to have a substituent, and the examples of the substituent include alkylgroup, having 1 to 6 carbons and fluorine atom

R^(a3) denotes a linear or branched alkylene group, a linear or branchedpoly(alkyleneoxy) group, a linear or branched unsaturated hydrocarbongroup, a carbonyl group, a carbonyl group-containing alkylene group, acarboxyl group-containing alkylene group, a carbamoyl group-containingalkylene group, or a group shown below. Examples of the alkylene groupinclude an ethylene group, a propylene group, and a butylene group, andexamples of the poly(alkyleneoxy) group include a poly(ethyleneoxy)group and a poly(propyleneoxy) group. Examples of the unsaturatedhydrocarbon group include a propenylene group, a methylpropenylenegroup, and a butenylene group.

When R^(a3) is the above-mentioned polyvalent group, R^(a4) denotes ahydrogen atom, an alkyl group having 1 to 4 carbons, an alkoxy grouphaving 1 to 4 carbons, a halogen atom, a nitro group, a cyano group, amercapto group, a lower alkylcarboxyl group, a carboxyl group, or acarbamoyl group.

R^(a5) denotes an oxygen atom, a sulfur atom, a methylene group, NH, SO,SO₂, C(CF₃)₂, or, C(CH₃)₂.

R^(a6) denotes an alkyl group having 1 to 4 carbons or an aryl group,and n is an integer of 0 to 2,000. R^(a7) denotes an alkyl group having1 to 4 carbons, an aryl group, or a monovalent group having thestructure below. In the formula, R^(a8) denotes an alkyl group having 1to 4 carbons or an aryl group, and m is an integer of 0 to 100.

Examples of the compound represented by Formula (1) include3-ethyl-3-hydroxymethyloxetane (OXT-101: manufactured by Toagosei Co.,Ltd.), 3-ethyl-3-(2-ethylhexyloxymethyl)oxetane (OXT-212: manufacturedby Toagosei Co., Ltd.), and 3-ethyl-3-phenoxymethyloxetane (OXT-211:manufactured by Toagosei Co., Ltd.). Examples of the compoundrepresented by Formula (2) include1,4-bis[(3-ethyl-3-oxetanylmethoxy)methyl]benzene (OXT-121: ToagoseiCo., Ltd.). Examples of the compound represented by Formula (3) includebis(3-ethyl-3-oxetanylmethyl)ether (OXT-221: Toagosei Co., Ltd.).

Examples of the compound having 3 to 4 oxetane rings in the moleculeinclude compounds represented by Formula (4) below.

In Formula (4), R^(a1) denotes the same as in Formula (1) above.Furthermore, examples of R^(a9), which is a polyvalent linking group,include a branched alkylene group having 1 to 12 carbons such as a grouprepresented by A to C below, a branched poly(alkyleneoxy) group such asa group represented by D below, and a branched polysiloxane group suchas a group represented by E below. j is 3 or 4.

In the above A, R^(a10) denotes a methyl group, an ethyl group, or apropyl group. Furthermore, in the above D, p is an integer of 1 to 10.

Moreover, as another embodiment of the oxetane compound that can besuitably used in the present invention, a compound having an oxetanering on a side chain, represented by Formula (5) below, can be cited.

In Formula (5), R^(a1) and R^(a8) denote the same as in theabove-mentioned formulae. R^(a11) is an alkyl group having 1 to 4carbons such as a methyl group, an ethyl group, a propyl group, or abutyl group, or a trialkylsilyl group, and r is 1 to 4.

Such compounds having an oxetane ring are described in detail inparagraph Nos. (0021) to (0084) of JP-A-2003-341217 above, and thecompounds described here may be suitably used in the present invention.

The oxetane compounds described in JP-A-2004-91556 can be used in thepresent invention. The details are described in paragraph Nos. (0022) to(0058).

Among the oxetane compounds used in the present invention, from theviewpoint of ink composition viscosity and tackiness, it is preferableto use a compound having one oxetane ring.

The ink composition of the present invention may comprise only one typeof cationically polymerizable compound or two or more types thereof incombination, but from the viewpoint of suppressing effectively shrinkageduring ink curing, it is preferable to use a combination of a vinylether compound and at least one type of compound selected from theoxetane compounds and the epoxy compounds.

The content of (B) the cationically polymerizable compound in the inkcomposition is suitably in the range of 10 to 95 wt % relative to thetotal solids content of the composition, preferably 30 to 93 wt %, andmore preferably 50 to 90 wt %. In the present invention, the solidscontent means the composition that obtained by eliminating the volatilecompound such as solvent, which will be described later, from the inkcomposition.

(C) Colorant

The colorant that can be used in the present invention is notparticularly limited, but a pigment and an oil-soluble dye that haveexcellent weather resistance and rich color reproduction are preferable,and it may be selected from any known colorant such as a soluble dye. Itis preferable that the colorant that can be suitably used in the inkcomposition or the inkjet recording ink composition of the presentinvention does not function as a polymerization inhibitor in apolymerization reaction, which is a curing reaction. This is because thesensitivity of the curing reaction by actinic radiation should not bedegraded.

(C-1) Pigment

The pigment that can be used in the present invention is notparticularly limited and, for example, organic and inorganic pigmentshaving the numbers below described in the Color Index may be used.

That is, as a red or magenta pigment, Pigment Red 3, 5, 19, 22, 31, 38,43, 48:1, 48:2, 48:3, 48:4, 48:5, 49:1, 53:1, 57:1, 57:2, 58:4, 63:1,81, 81:1, 81:2, 81:3, 81:4, 88, 104, 108, 112, 122, 123, 144, 146, 149,166, 168, 169, 170, 177, 178, 179, 184, 185, 208, 216, 226, or 257,Pigment Violet 3, 19, 23, 29, 30, 37, 50, or 88, and Pigment Orange 13,16, 20, or 36; as a blue or cyan pigment, Pigment Blue 1, 15, 15:1,15:2, 15:3, 15:4, 15:6, 16, 17-1, 22, 27, 28, 29, 36, or 60; as a greenpigment, Pigment Green 7, 26, 36, or 50; as a yellow pigment, PigmentYellow 1, 3, 12, 13, 14, 17, 34, 35, 37, 55, 74, 81, 83, 93, 94, 95, 97,108, 109, 110, 137, 138, 139, 153, 154, 155, 157, 166, 167, 168, 180,185, or 193; as a black pigment, Pigment Black 7, 28, or 26; as a whitepigment, Pigment White 6, 18, or 21, etc. may be used according to theintended application.

(C-2) Oil-Soluble Dye

The oil-soluble dye that can be used in the present invention isexplained below.

The oil-soluble dye that can be used in the present invention means adye that is substantially insoluble in water. Specifically, thesolubility in water at 25° C. (the mass of dye that can be dissolved in100 g of water) is no greater than 1 g, preferably no greater than 0.5g, and more preferably no greater than 0.1 g. Therefore, the oil-solubledye means a so-called water-insoluble pigment or an oil-soluble dye, andamong these the oil-soluble dye is preferable.

In the present invention, the oil-soluble dye may be used singly or in acombination of two or more types. Furthermore, another colorant such asa water-soluble dye, a disperse dye, or a pigment may be contained asnecessary in a range that does not interfere with the effects of thepresent invention.

Among the oil-soluble dyes that can be used in the present invention, asa yellow dye, any may be used. Examples thereof include aryl or heterylazo dyes having a coupling component such as a phenol, a naphthol, ananiline, a pyrazolone, a pyridone, or an open-chain active methylenecompound; azomethine dyes having a coupling component such as anopen-chain active methylene compound; methine dyes such as benzylidenedyes and monomethineoxonol dyes; quinone dyes such as naphthoquinonedyes and anthraquinone dyes; and other dye species such asquinophthalone dyes, nitro/nitroso dyes, acridine dyes, and acridinonedyes.

Among the above-mentioned oil-soluble dyes that can be used in thepresent invention, as a magenta dye, any may be used. Examples thereofinclude aryl or heteryl azo dyes having a coupling component such as aphenol, a naphthol, or an aniline; azomethine dyes having a couplingcomponent such as a pyrazolone or a pyrazolotriazole; methine dyes suchas arylidene dyes, styryl dyes, merocyanine dyes, and oxonol dyes;carbonium dyes such as diphenylmethane dyes, triphenylmethane dyes, andxanthene dyes; quinone dyes such as naphthoquinones, anthraquinones, oranthrapyridones; and condensed polycyclic dyes such as dioxazine dyes.

Among the oil-soluble dyes that can be used in the present invention, asa cyan dye, any may be used. Examples thereof include indoaniline dyes,indophenol dyes, and azomethine dyes having a coupling component such asa pyrrolotriazole; polymethine dyes such as cyanine dyes, oxonol dyes,and merocyanine dyes; carbonium dyes such as diphenylmethane dyes,triphenylmethane dyes, and xanthene dyes; phthalocyanine dyes;anthraquinone dyes; aryl or heteryl azo dyes having a coupling componentsuch as a phenol, a naphthol, or an aniline; and indigo/thioindigo dyes.

The above-mentioned dyes may be dyes that exhibit respective colors ofyellow, magenta, and cyan only after a part of the chromophoredissociates, and in that case the counter cation may be an inorganiccation such as an alkali metal or ammonium, may be an organic cationsuch as pyridinium or a quaternary ammonium salt, or may be a polymercation having the above cation as a partial structure.

Although not limited to the following, preferred specific examplesthereof include CI Solvent Black 3, 7, 27, 29, and 34; CI Solvent Yellow14, 16, 19, 29, 30, 56, 82, 93, and 162; CI Solvent Red 1, 3, 8, 18, 24,27, 43, 49, 51, 72, 73, 109, 122, 132, and 218; CI Solvent Violet 3; CISolvent Blue 2, 11, 25, 35, 38, 67, and 70; CI Solvent Green 3 and 7;and CI Solvent Orange 2. Particularly preferred examples thereof includeNubian Black PC-0850, Oil Black HBB, Oil Yellow 129, Oil Yellow 105, OilPink 312, Oil Red 5B, Oil Scarlet 308, Vali Fast Blue 2606, Oil Blue BOS(manufactured by Orient Chemical Industries, Ltd.), Aizen Spilon BlueGNH (manufactured by Hodogaya Chemical Co., Ltd.), Neopen Yellow 075,Neopen Magenta SE1378, Neopen Blue 808, Neopen Blue FF4012, and NeopenCyan FF4238 (manufactured by BASF).

In the present invention, a disperse dye may be used in a range thatenables it to be dissolved in a water-immiscible organic solvent.Specific preferred examples thereof include CI Disperse Yellow 5, 42,54, 64, 79, 82, 83, 93, 99, 100, 119, 122, 124, 126, 160, 184:1, 186,198, 199, 201, 204, 224, and 237; CI Disperse Orange 13, 29, 31:1, 33,49, 54, 55, 66, 73, 118, 119, and 163; CI Disperse Red 54, 60, 72, 73,86, 88, 91, 92, 93, 111, 126, 127, 134, 135, 143, 145, 152, 153, 154,159, 164, 167:1, 177, 181, 204, 206, 207, 221, 239, 240, 258, 277, 278,283, 311, 323, 343, 348, 356, and 362; CI Disperse Violet 33; CIDisperse Blue 56, 60, 73, 87, 113, 128, 143, 148, 154, 158, 165, 165:1,165:2, 176, 183, 185, 197, 198, 201, 214, 224, 225, 257, 266, 267, 287,354, 358, 365, and 368; and CI Disperse Green 6:1 and 9.

Particularly preferred examples of the oil-soluble dye include azo andazomethine dyes represented by Formulae (1) and (2) below. Dyesrepresented by Formula (2) below are known, in the photographic materialarea, as dyes that are generated from a coupler and a developing agentby oxidation.

In Formulae (1) and (2) above, R¹, R², R³ and R⁴ independently denote ahydrogen atom, a halogen atom, an aliphatic group, an aromatic group, aheterocyclic group, a cyano group, a hydroxyl group, a nitro group, anamino group, an alkylamino group, an alkoxy group, an aryloxy group, anamide group, an arylamino group, a ureido group, a sulfamoylamino group,an alkylthio group, an arylthio group, an alkoxycarbonylamino group, asulfonamide group, a carbamoyl group, a sulfamoyl group, a sulfonylgroup, an alkoxycarbonyl group, a heterocyclooxy group, an azo group, anacyloxy group, a carbamoyloxy group, a silyloxy group, anaryloxycarbonyl group, an aryloxycarbonylamino group, an imide group, aheterocyclothio group, a sulfinyl group, a phosphoryl group, an acylgroup, a carboxyl group, or a sulfo group.

In Formulae (1) and (2) above, in particular, R² is preferably, amongthe above-mentioned substituents, a hydrogen atom, a halogen atom, analiphatic group, an alkoxy group, an aryloxy group, an amide group, aureido group, a sulfamoylamino group, an alkoxycarbonylamino, or asulfonamide group.

In the present specification, the aliphatic group denotes an alkylgroup, a substituted alkyl group, an alkenyl group, a substitutedalkenyl group, an alkynyl group, a substituted alkynyl group, an aralkylgroup, or a substituted aralkyl group. The aliphatic group may have abranch or form a ring. The number of carbon atoms of the aliphatic groupis preferably 1 to 20, and more preferably 1 to 18. The aryl moiety ofthe aralkyl group and the substituted aralkyl group is preferably phenylor naphthyl, and particularly preferably phenyl. Examples of thesubstituents of the alkyl moieties of the substituted alkyl group, thesubstituted alkenyl group, the substituted alkynyl group, and thesubstituted aralkyl group include the substituents cited for explanationof R¹ to R⁴. Examples of the substituents of the aryl moiety of thesubstituted aralkyl group are the same as those of the substituent ofthe substituted aryl group below.

In the present specification, the aromatic group means an aryl group anda substituted aryl group. The aryl group is preferably phenyl ornaphthyl, and particularly preferably phenyl. The aryl moiety of thesubstituted aryl group is the same as that of the above-mentioned arylgroup. Examples of the substituent of the substituted aryl group includesubstituents cited for explanation of R¹ to R⁴.

In Formulae (1) and (2) above, A denotes —NR⁵R⁶ or a hydroxyl group, andR⁵ and R⁶ independently denote a hydrogen atom, an aliphatic group, anaromatic group, or a heterocyclic group. A is preferably —NR⁵R⁶. R⁵ andR⁶ may be bonded together to form a ring. R⁵ and R⁶ preferably eachdenote a hydrogen atom, an alkyl group, a substituted alkyl group, anaryl group, or a substituted aryl group, and most preferably a hydrogenatom, an alkyl group having 1 to 18 carbon atoms, or a substituted alkylgroup having 1 to 18 carbon atoms.

In Formula (2) above, B¹ denotes ═C(R³)— or ═N—, and B² denotes —C(R⁴)═or —N═. It is preferable that B¹ and B² are not —N═ at the same time,and it is more preferable that B¹ is ═C(R³)— and B² is —C(R⁴)═. Any ofR¹ and R⁵, R³ and R⁶, and R¹ and R² may be bonded together to form anaromatic ring or a hetero ring.

In Formula (1) above, Y denotes an unsaturated heterocyclic group. Y ispreferably a five-membered or six-membered unsaturated hetero ring. Thehetero ring may be condensed with an aliphatic ring, an aromatic ring,or another hetero ring. Examples of the hetero atom of the hetero ringinclude N, O, and S.

Preferred examples of the above-mentioned unsaturated hetero ringinclude a pyrazole ring, an imidazole ring, a thiazole ring, anisothiazole ring, a thiadiazole ring, a thiophene ring, a benzothiazolering, a benzoxazole ring, a benzoisothiazole ring, a pyrimidine ring, apyridine ring, and a quinoline ring. It is also possible for theunsaturated heterocyclic group to have a substituent cited above as R¹to R⁴.

In Formula (2) above, X denotes a color photographic coupler residue.Preferred examples of the color photographic coupler residue are asfollows.

Yellow couplers: U.S. Pat. Nos. 3,933,501, 4,022,620, 4,326,024, and4,401,752, 4,428,961, JP-B-58-10739, GB Pat. Nos. 1,425,020 and1,476,760, U.S. Pat. Nos. 3,973,968, 4,314,023, and 4,511,649, and EPPat. No. 249,473A and couplers represented by Formulae (I) and (II) inU.S. Pat. No. 502,424A; couplers represented by Formulae (1) and (2) inEP Pat. No. 513,496A (in particular, Y-28 on page 18); couplersrepresented by Formula (I) of Claim 1 in EP Pat. No. 568,037A; couplersrepresented by Formula (I) of lines 45 to 55 in Column 1 in U.S. Pat.No. 5,066,576; couplers represented by Formula (I) in Paragraph 0008 inJP-A-4-274425; couplers of Claim 1 on page 40 in EP Pat. No. 498,381A1(in particular, D-35 on page 18); couplers represented by Formula (Y) onpage 4 in EP Pat. No. 447,969A1 (in particular, Y-1 (page 17) and Y-54(page 41)); and couplers represented by Formulae (II) to (IV) on lines36 to 58 of Column 7 in U.S. Pat. No. 4,476,219 (in particular, II-17and 19 (Column 17), and II-24 (Column 19)).

Magenta couplers: U.S. Pat. Nos. 4,310,619 and 4,351,897, EP Pat. No.73,636, U.S. Pat. Nos. 3,061,432 and 3,725,067, Research Disclosure No.24220 (June, 1984) and No. 24230 (June, 1984), JP-A-60-33552,JP-A-60-43659, JP-A-61-72238, JP-A-60-35730, JP-A-55-118034,JP-A-60-185951, U.S. Pat. Nos. 4,500,630, 4,540,654, and 4,556,630,WO88/04795, JP-A-3-39737 (L-57 (page 11, lower right), L-68 (page 12,lower right), L-77 (page 13, lower right)), EP Pat. No. 456,257 [A-4]-63(p. 134), [A-4]-73, -75 (p. 139), EP Pat. No. 486,965 M-4, M-6 (p. 26),M-7 (p. 27), EP Pat. No. 571,959 M-45 (p. 19), JP-A-5-204106 M-1 (p. 6),and JP-A-4-362631 paragraph No. 0237, M-22, and U.S. Pat. Nos. 3,061,432and 3,725,067.

Cyan coupler: U.S. Pat. Nos. 4,052,212, 4,146,396, 4,228,233, and4,296,200, EP Pat. No. 73,636, JP-A-4-204843, CX-1, 3, 4, 5, 11, 12, 14,15 (pp. 14 to 16); JP-A-4-43345 C-7, 10 (p. 35), 34, 35 (p. 37), (1-1),(1-17) (pp. 42 to 43); and couplers represented by Formula (Ia) or (Ib)of Claim 1 in JP-A-6-67385.

Furthermore, couplers described in JP-A-62-215272 (p. 91), JP-A-2-33144(p. 3 and 30), EP 355,660A (p. 4, 5, 45 and 47) are also useful.

Among the oil-soluble dyes represented by Formula (1) above, the magentadyes particularly preferably used are dyes represented by Formula (3)below.

In Formula (3) above, Z¹ denotes an electron-attracting group having aHammett substituent constant σp value of equal to or greater than 0.20.Z¹ is preferably an electron-attracting group having a σp value of atleast 0.30 but no greater than 1.0. Preferred specific examples of thesubstituent include electron-attracting substituents that are describedlater, and among them an acyl group having 2 to 12 carbons, an alkyloxycarbonyl group having 2 to 12 carbons, a nitro group, a cyano group, analkylsulfonyl group having 1 to 12 carbons, an arylsulfonyl group having6 to 18 carbons, a carbamoyl group having 1 to 12 carbons, and ahaloalkyl group having 1 to 12 carbons are preferable. A cyano group, analkylsulfonyl group having 1 to 12 carbons, and an arylsulfonyl grouphaving 6 to 18 carbons are particularly preferable, and a cyano group ismost preferable.

In Formula (3) above, Z² denotes a hydrogen atom, an aliphatic group, oran aromatic group.

In Formula (3) above, R¹ to R⁶ are the same as the corresponding ones ofFormula (1) above.

In Formula (3) above, Q denotes a hydrogen atom, an aliphatic group, anaromatic group, or a heterocyclic group. Among them, Q is preferably agroup formed from a group of non-metal atoms necessary to form a 5- to8-membered ring. Among them an aromatic group and a heterocyclic groupare particularly preferable. The 5- to 8-membered ring may besubstituted, may be a saturated ring, or may have an unsaturated bond.Preferred examples of the non-metal atom include a nitrogen atom, anoxygen atom, a sulfur atom, and a carbon atom. Specific examples of suchring structures include a benzene ring, a cyclopentane ring, acyclohexane ring, a cycloheptane ring, a cyclooctane ring, a cyclohexenering, a pyridine ring, a pyrimidine ring, a pyrazine ring, a pyridazinering, a triazine ring, an imidazole ring, a benzoimidazole ring, anoxazole ring, a benzoxazole ring, an oxane ring, a sulfolane ring, and athiane ring, and in a case where these rings have a further substituent,examples of the substituent include groups cited as examples ofsubstituents R¹ to R⁴ in Formula (1) above.

Preferred structures of the compounds represented by Formula (3) aboveare described in JP-A-2001-335714.

Among the dyes represented by Formula (2) above, the magenta dyeparticularly preferably employs a dye represented by Formula (4) below.

In Formula (4) above, G denotes a hydrogen atom, an aliphatic group, anaromatic group, a heterocyclic group, a cyano group, an alkoxy group, anaryloxy group, an alkylthio group, an arylthio group, an ester group, anamino group, a carbamoyl group, a sulfonyl group, a sulfamoyl group, aureido group, a urethane group, an acyl group, an amide group, or asulfonamide group.

In Formula (4) above, R¹, R², A, B¹, and B² are the same as thecorresponding ones of Formula (2) above, and preferred ranges are alsothe same.

In Formula (4) above, L denotes an atomic group forming a five-memberedor six-membered nitrogen-containing hetero ring, which may besubstituted with at least one of an aliphatic group, an aromatic group,a heterocyclic group, a cyano group, an alkoxy group, an aryloxy group,an alkylthio group, an arylthio group, an ester group, an amino group, acarbamoyl group, a sulfonyl group, a sulfamoyl group, a ureido group, aurethane group, an acyl group, an amide group, and a sulfonamide group,and this hetero ring may further form a condensed ring with anotherring.

With regard to compounds represented by Formula (4) above, A ispreferably —NR⁵R⁶, and L preferably forms a five-memberednitrogen-containing hetero ring; examples of the five-memberednitrogen-containing hetero ring include an imidazole ring, a triazolering, and a tetrazole ring.

Among the dyes represented by Formula (1) and Formula (2) above,compound examples (M-0, M-1 to 6, a-21 to 25) for a magenta dye areshown below, but these are only for explaining the present invention indetail, and the present invention should not be construed as beinglimited thereto.

In the present invention, M-0, M-4, M-6, or a-21 may be preferably used,and M-4, M-6, or a-21 may be particularly preferably used.

TABLE 1

Dye R₁ R₂ R₃ R₄ a-21 A A

a-22

A

a-23

B

a-24

a-25

C

C₈H₁₇(t) A: 

B: 

C: 

Other compound examples of the colorant that can be used in the presentinvention include those described in JP-A-2001-240763, 2001-181549, andJP-A-2001-335714, but the present invention should not be construed asbeing limited thereto.

The compound represented by Formula (3) above may be synthesized byreference to a method described in, for example, JP-A-2001-335714 orJP-A-55-161856. The compound represented by Formula (4) above may besynthesized by reference to a method described in, for example,JP-A-4-126772, JP-B-7-94180, or JP-A-2001-240763.

Among the dyes represented by Formula (2) above, as a cyan dye apyrrolotriazole azomethine dye represented by Formula (5) below isparticularly preferably used.

In Formula (5) above, A, R¹, R², B¹, and B² are the same as thecorresponding ones of Formula (2) above, and preferred ranges thereofare also the same.

In Formula (5) above, Z³ and Z⁴ are independently the same as G inFormula (4) above. Z³ and Z⁴ may be bonded together to form a ringstructure. One in which Z³ is an electron-attracting group having aHammett substituent constant σp value of equal to or greater than 0.30exhibits a sharp absorption and is more preferable. Moreover, one inwhich Z³ is an electron-attracting group having a Hammett substituentconstant σp value of equal to or greater than 0.45 is more preferable,and an electron-attracting group having a Hammett substituent constantσp value of equal to or greater than 0.60 is most preferable.Furthermore, one in which the sum of the Hammett substituent constant σpvalues of Z³ and Z⁴ is equal to or greater than 0.70 exhibits excellenthue of a cyancolor, and is more preferable.

In Formula (5) above, M is an atomic group forming a 1,2,4-triazole ringthat is condensed with the 5-membered ring of Formula (5) above; eitherone of the two atoms B³ and B⁴ at the sites of condensation with the5-membered ring is a nitrogen atom, and the other is a carbon atom.

The compound represented by Formula (5) above is preferably used as acyan dye, but it may be used as a magenta dye by changing a substituent.

The Hammett substituent constant σp value used in the presentspecification is now explained. The Hammett rule is an empirical ruleproposed by L. P. Hammett in 1935 in order to quantitatively deal withthe influence of a substituent on a reaction or equilibrium of a benzenederivative, and the validity thereof is currently widely recognized. Aσp value and a am value are required for the substituent constant in theHammett rule, and details of these values can be referred to in manygeneral books, for example, ‘Lange's Handbook of Chemistry’, Ed. by J.A. Dean, 12th edition, 1979 (Mc Graw-Hill) or ‘Kagakuno Ryouiki’(Journal of Japanese Chemistry), special issue, 122, pp. 96 to 103, 1979(Nankodo Co., Ltd.). In the present invention, the substituents arelimited or explained using the Hammett substituent constant σp, but thisdoes not mean that they are limited to substituents whose values aredescribed in published references, and a substituent whose value is notpublished in the references but is included in the range if it ismeasured in accordance with the Hammett rule is of course included.Among Formulae (1) to (5) above, those that are not benzene derivativesare also included, but the σp value is used as a scale showing theelectronic effect of the substituent, irrespective of the position ofsubstitution. The σp value in the present invention is used with theabove-mentioned meaning.

Examples of electron-attracting groups having a Hammett substituentconstant σp value of equal to or greater than 0.60 include a cyanogroup, a nitro group, an alkylsulfonyl group (e.g. a methanesulfonylgroup), and an arylsulfonyl group (e.g. a benzenesulfonyl group).Examples of electron-attracting groups having a Hammett σp value ofequal to or greater than 0.45 include, in addition to the above, an acylgroup (e.g. an acetyl group), an alkoxycarbonyl group (e.g. adodecyloxycarbonyl group), an aryloxycarbonyl group (e.g.m-chlorophenoxycarbonyl), an alkylsulfinyl group (e.g.n-propylsulfinyl), an arylsulfinyl group (e.g. phenylsulfinyl), asulfamoyl group (e.g. N-ethylsulfamoyl, N,N-dimethylsulfamoyl), and ahaloalkyl group (e.g. trifluoromethyl).

Examples of electron-attracting groups having a Hammett substituentconstant σp value of equal to or greater than 0.30 include, in additionto the above, an acyloxy group (e.g. acetoxy), a carbamoyl group (e.g.N-ethylcarbamoyl, N,N-dibutylcarbamoyl), a haloalkoxy group (e.g.trifluoromethyloxy), a haloaryloxy group (e.g. pentafluorophenyloxy), asulfonyloxy group (e.g. a methylsulfonyloxy group), a haloalkylthiogroup (e.g. difluoromethylthio), an aryl group substituted with two ormore electron-attracting groups having a σp value of equal to or greaterthan 0.15 (e.g. 2,4-dinitrophenyl, pentachlorophenyl), and a hetero ring(e.g. 2-benzooxazolyl, 2-benzothiazolyl, 1-phenyl-2-benzimidazolyl).Specific examples of electron-attracting groups having a σp value ofequal to or greater than 0.20 include, in addition to the above, ahalogen atom.

Furthermore, in the present invention, an oil-soluble dye represented byFormula (A-I) below can be used preferably.

In Formula (A-I): X₁, X₂, X₃, and X₄ independently denote a groupselected from —SO-Z, —SO₂-Z, —SO₂NR₁R₂, —CONR₁R₂, —CO₂R₁, and a sulfogroup. Here, Z denotes a substituted or unsubstituted alkyl group, asubstituted or unsubstituted cycloalkyl group, a substituted orunsubstituted alkenyl group, a substituted or unsubstituted aralkylgroup, a substituted or unsubstituted aryl group, or a substituted orunsubstituted heterocyclic group. R₁ and R₂ independently denote ahydrogen atom, a substituted or unsubstituted alkyl group, a substitutedor unsubstituted cycloalkyl group, a substituted or unsubstitutedalkenyl group, a substituted or unsubstituted aralkyl group, asubstituted or unsubstituted aryl group, or a substituted orunsubstituted heterocyclic group, provided that R₁ and R₂ are not bothhydrogen atoms. M denotes a hydrogen atom, a metal element, a metaloxide, a metal hydroxide, or a metal halide. Y₁, Y₂, Y₃, and Y₄independently denote a hydrogen atom or a monovalent substituent. a₁ toa₄ and b₁ to b₄ denote the numbers of X₁ to X₄ and Y₁ to Y₄, andindependently denote an integer of 0 to 4, provided that the sum totalof a₁ to a₄ is equal to or greater than 2.

Among the oil-soluble dyes represented by Formula (A-I) above, anoil-soluble dye represented by Formula (A-II) below may particularlypreferably be used.

In Formula (A-II): X₁₁ to X₁₄, Y₁₁ to Y₁₈, and M are the same as X₁ toX₄, Y₁ to Y₄, and M in Formula (A-I) respectively. a₁₁ to a₁₄independently denote an integer of 1 or 2.

As a specific example of Formula (A-II) above, a compound example(AII-17) is cited, but this is for explaining the present invention indetail, and the present invention should not be construed as beinglimited thereto.

Compound No. M X a AII-17 Cu

1 AII-18 Cu

1 AII-19 Cu

1 AII-20 Cu

1 AII-21 Cu

1 AII-22 Cu

1 AII-23 Cu

1

In the present invention, it is preferable to use an oil-soluble dyehaving an oxidation potential that is more noble than 1.0 V (SCE). Themore noble the oxidation potential, the more preferable it is; it ismore preferable to use one having an oxidation potential more noble than1.1 V (SCE), and it is most preferable to use one having an oxidationpotential more noble than 1.2 V (SCE).

The oxidation potential value (Eox) can be easily measured by oneskilled in the art and a method therefor is described in, for example,P. Delahay, ‘New Instrumental Methods in Electrochemistry’, IntersciencePublishers (1954), A. J. Bard et al., ‘Electrochemical Methods’, JohnWiley & Sons (1980), and Akira Fujishima et al., ‘DenkikagakuSokuteihou’ (Electrochemical Measurement Methods), Gihodo Shuppan Sha(1984).

More specifically, a test sample is dissolved to give a concentration of1×10⁻⁴ to 1×10⁻⁶ mol/L in a solvent such as dimethylformamide oracetonitrile containing a supporting electrolyte such as sodiumperchlorate or tetrapropylammonium perchlorate, an oxidation wave whensweeping toward the oxidation side (noble side) using carbon (GC) as aworking electrode and a rotating platinum electrode as the counterelectrode using cyclic voltammetry or direct current polarographicequipment is approximated to a straight line, and the oxidationpotential of the midpoint of a line segment formed between anintersection point of the straight line and a residual current/potentialstraight line and an intersection point of the straight line and asaturated current straight line (or an intersection point with astraight line parallel to the ordinate passing through the potentialpeak value) is measured as a value relative to the SCE (saturatedcalomel electrode). This value sometimes deviates by on the order oftens of millivolts due to the effect of a liquid junction potential, theliquid resistance of the sample solution, or the like, but thereproducibility of the potential can be guaranteed by adding a standardsample (for example, hydroquinone). The support electrolyte and solventused may be selected appropriately according to the oxidation potentialand the solubility of the test sample. The support electrolyte andsolvent that can be used here may be referred to in Akira Fujishima etal., ‘Denkikagaku Sokuteihou’ (Electrochemical Measurement Methods),Gihodo Shuppan Sha (1984), pp. 101 to 118.

In the concentration range of the above-mentioned measurement solventand a phthalocyanine compound sample, the oxidation potential of adisassociated state is measured.

The value of Eox represents the ease of electron transfer from a sampleto an electrode; the larger the value (the more noble the oxidationpotential), the more difficult it is for electrons to transfer from thesample to the electrode, in other words, the more difficult it is tooxidize.

If a dye having a low oxidation potential is used, polymerization isgreatly inhibited by the dye, and the curability is degraded. When a dyehaving a noble oxidation potential is used, there is hardly anyinhibition of polymerization.

The colorant that can be used in the present invention is preferablyadded to the ink composition or the inkjet recording ink composition ofthe present invention and then dispersed in the ink to an appropriatedegree. For dispersion of the colorant, for example, a dispersingmachine such as a ball mill, a sand mill, an attritor, a roll mill, anagitator, a Henschel mixer, a colloidal mill, an ultrasonic homogenizer,a pearl mill, a wet type jet mill, or a paint shaker may be used.

When carrying out dispersion of the colorant, a dispersant may be added.The type of dispersant is not particularly limited, but it is preferableto use a polymeric dispersant, and examples of the polymeric dispersantinclude the Solsperse series manufactured by Avecia. Furthermore, as adispersion adjuvant, it is also possible to use a synergist, accordingto the various types of pigment. In the present invention, thedispersant and dispersion adjuvant are preferably added at 1 to 50 partsby weight relative to 100 parts by weight of the pigment.

The colorant may be added directly to the ink composition of the presentinvention, but in order to improve dispersibility it may be added inadvance to a solvent or a dispersing medium such as a polymerizablecompound used in the present invention. In the present invention, inorder to avoid the problem of the solvent resistance being degraded whenthe solvent remains in the cured image and the VOC (Volatile OrganicCompound) problem of the residual solvent, it is preferable to add thecolorant to a polymerizable compound. As a polymerizable compound used,it is preferable in terms of dispersion suitability to select a monomerhaving the lowest viscosity.

In the present invention, it is preferable for the average particle sizeof the colorant particles to be in the range of 0.005 to 0.5 μm, morepreferably 0.01 to 0.45 μm, and yet more preferably, 0.015 to 0.3 μm.Furthermore, the maximum particle size of the colorant is preferably 0.3to 10 μm, and more preferably 0.3 to 3 μm. In order to make the maximumparticle size of the colorant be in the above-mentioned range, thecolorant, the dispersant, and the dispersing medium are selected, anddispersion conditions and filtration conditions are set. By such controlof particle size, clogging of a head nozzle can be suppressed, and theink storage stability, the ink transparency, and the curing sensitivitycan be maintained.

The colorant is preferably added to the ink composition at 1 to 20 wt %of the total weight of the ink composition, and more preferably 2 to 15wt %.

(D) Sensitizer

The ink composition of the present invention may comprise (D) asensitizer for the purpose of improving the acid-generating efficiencyof the acid-generating compound and increasing the wavelength at whichit exhibits sensitivity. The sensitizer that can be used in the presentinvention is preferably one that sensitizes the acid-generating compoundby virtue of an electron transfer mechanism or an energy transfermechanism.

Examples of the sensitizer that can be used in the present inventioninclude those belonging to the types of compounds listed below andhaving an absorption wavelength in the wavelength region of 300 nm to450 nm.

Preferred examples of the sensitizer include those belonging to thetypes of compounds below and having an absorption wavelength at 350 nmto 450 nm.

Examples include polynuclear aromatic compounds (e.g. phenanthrene,anthracene, pyrene, perylene, triphenylene, a 9,10-dialkoxyanthracene),xanthenes (e.g. fluorescein, eosin, erythrosine, rhodamine B, rosebengal), thioxanthones (e.g. isopropylthioxanthone, diethylthioxanthone,chlorothioxanthone), cyanines (e.g. thiacarbocyanine, oxacarbocyanine),merocyanines (e.g. merocyanine, carbomerocyanine), phthalocyanines,thiazines (e.g. thionine, methylene blue, toluidine blue), acridines(e.g. acridine orange, chloroflavin, acriflavin), anthraquinones (e.g.anthraquinone), squariums (e.g. squarium), acridine orange, coumarins(e.g. 7-diethylamino-4-methylcoumarin), ketocoumarin, phenothiazines,phenazines, styrylbenzenes, azo compounds, diphenylmethane,triphenylmethane, distyrylbenzenes, carbazoles, porphyrin, spirocompounds, quinacridone, indigo, styryl, pyrylium compounds,pyrromethene compounds, pyrazolotriazole compounds, benzothiazolecompounds, barbituric acid derivatives, thiobarbituric acid derivatives,and compounds described in EP No. 568,993, U.S. Pat. Nos. 4,508,811 and5,227,227, JP-A-2001-125255, JP-A-11-271969, etc.

Among them, the acid-generating compound of the present invention ispreferably combined with a polynuclear aromatic compound (e.g.phenanthrene, anthracene, pyrene, perylene, triphenylene, a9,10-dialkoxyanthracene), a thioxanthone, a distyrylbenzene, astyrylbenzene, or a carbazole from the viewpoint of initiationefficiency, and most preferably with a distyrylbenzene, a styrylbenzene,a diphenylbutadiene, or a carbazole.

Furthermore, preferred examples of the sensitizer that can be used inthe present invention include compounds having any one of the skeletonsbelow.

Preferred specific examples of the sensitizer that can be used in thepresent invention include the compounds below.

From the viewpoint of the coloring properties of the ink, the content ofthe sensitizer (D) in the ink composition of the present invention ispreferably 0.01 to 20 wt % relative to the entire weight of the inkcomposition, more preferably 0.1 to 15 wt %, and yet more preferably 0.5to 10 wt %.

The sensitizer (D) may be used singly or in a combination of two or moretypes.

Furthermore, from the viewpoint of improvement in the decompositionratio of the acid-generating compound and transparency to irradiatinglight, the ratio of the acid-generating compound (A) to the sensitizer(D) contained in the ink composition is preferably A/D=100 to 0.05 as aratio by weight, more preferably A/D=50 to 0.1, and yet more preferablyA/D=10 to 0.5.

(E) Cosensitizer

The ink composition of the present invention preferably comprises acosensitizer. In the present invention, the cosensitizer has thefunction of further improving the sensitivity of the sensitizing dye toactinic radiation or the function of suppressing inhibition by oxygen ofpolymerization of a polymerizable compound, etc.

Examples of such a cosensitizer include amines such as compoundsdescribed in M. R. Sander et al., ‘Journal of Polymer Society’, Vol. 10,p. 3173 (1972), JP-B-44-20189, JP-A-51-82102, JP-A-52-134692,JP-A-59-138205, JP-A-60-84305, JP-A-62-18537, JP-A-64-33104, andResearch Disclosure No. 33825, and specific examples thereof includetriethanolamine, ethyl p-dimethylaminobenzoate, p-formyldimethylaniline,and p-methylthiodimethylaniline.

Other examples of the cosensitizer include thiols and sulfides such asthiol compounds described in JP-A-53-702, JP-B-55-500806, andJP-A-5-142772, and disulfide compounds of JP-A-56-75643, and specificexamples thereof include 2-mercaptobenzothiazole, 2-mercaptobenzoxazole,2-mercaptobenzimidazole, 2-mercapto-4(3H)-quinazoline, andβ-mercaptonaphthalene.

Yet other examples of the cosensitizer include amino acid compounds(e.g. N-phenylglycine, etc.), organometallic compounds described inJP-B-48-42965 (e.g. tributyltin acetate, etc.), hydrogen-donatingcompounds described in JP-B-55-34414, sulfur compounds described inJP-A-6-308727 (e.g. trithiane, etc.), phosphorus compounds described inJP-A-6-250387 (diethylphosphite, etc.), and Si—H or Ge—H compoundsdescribed in JP-A-8-54735.

(F) Other Polymerizable Compound

The ink composition of the present invention may employ the cationicallypolymerizable compound (B) and another polymerizable compound incombination. Examples of polymerizable compounds that can be used incombination in the present invention include radically polymerizablecompounds. As the radically polymerizable compounds, photocurablematerials employing a photopolymerizable composition described inJP-A-7-159983, JP-B-7-31399, JP-A-8-224982, JP-A-10-863, JP-A-9-80675,etc. are known (JP-B denotes a Japanese examined patent applicationpublication).

The radically polymerizable compounds that can be used in the presentinvention are compounds having at least one radically polymerizablecarbon-carbon double bond (ethylenically unsaturated bond), may be anycompound as long as it has one radically polymerizable ethylenicallyunsaturated bond in the molecule, and include chemical configurationssuch as monomer, oligomer, and polymer. The radically polymerizablecompounds may be used singly or may be used in a combination of two ormore types at any ratio in order to improve desired properties.

Examples of the polymerizable compound having a radically polymerizableethylenically unsaturated bond include unsaturated carboxylic acids suchas acrylic acid, methacrylic acid, itaconic acid, crotonic acid,isocrotonic acid, and maleic acid, and salts thereof, anhydrides havingan ethylenically unsaturated group, acrylonitrile, styrene, and varioustypes of radically polymerizable compounds such as unsaturatedpolyesters, unsaturated polyethers, unsaturated polyamides, andunsaturated urethanes.

Specific examples thereof include acrylic acid derivatives such as2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, butoxyethyl acrylate,carbitol acrylate, cyclohexyl acrylate, tetrahydrofurfuryl acrylate,benzyl acrylate, diacetone acrylamide, and an epoxyacrylate; methacrylicderivatives such as methyl methacrylate, n-butyl methacrylate,2-ethylhexyl methacrylate, lauryl methacrylate, allyl methacrylate,glycidyl methacrylate, benzyl methacrylate, and dimethylaminomethylmethacrylate; and allyl compound derivatives such as allyl glycidylether. More specifically, commercial products, radically polymerizableor crosslinking monomers, oligomers, and polymers known in the art suchas those described in ‘Kakyozai Handobukku’ (Crosslinking AgentHandbook), Ed. S. Yamashita (Taiseisha, 1981); ‘UV•EB Koka Handobukku’(UV•EB Curing Handbook (Starting Materials) Ed. K. Kato (KobunshiKankoukai, 1985); ‘UV•EB Koka Gijutsu no Oyo to Shijyo’ (Application andMarket of UV•EB Curing Technology’, p. 79, Ed. Rad Tech (CMC, 1989); andE. Takiyama ‘Poriesuteru Jushi Handobukku’ (Polyester Resin Handbook),(The Nikkan Kogyo Shimbun Ltd., 1988) can be used.

It is preferable to use the radically polymerizable compound and thecationically polymerizable compound in combination since, due to highsensitivity characteristic of radical polymerization and low volumeshrinkage characteristic of cationic polymerization, a printed materialor a lithographic printing plate having both high sensitivity andadhesion is obtained.

(G) Other Polymerization Initiator

The ink composition of the present invention may employ (G) anotherpolymerization initiator in combination. As said other polymerizationinitiator that can be used in the present invention, known radicalpolymerization initiators can be used in combination. Thesepolymerization initiators may be used singly or in a combination of twoor more types.

The radical polymerization initiator that can be used in the inkcomposition of the present invention is a compound that forms apolymerization initiating species by absorbing external energy. Theexternal energy used for initiating polymerization can be broadlydivided into heat and actinic radiation, and a thermal polymerizationinitiator and a photopolymerization initiator are used respectively.Examples of the actinic radiation include γ rays, β rays, an electronbeam, UV rays, visible light, and IR rays.

<Radical Polymerization Initiator>

Examples of the radical polymerization initiator that can be used in thepresent invention include (a) aromatic ketones, (b) aromatic onium saltcompounds, (c) organic peroxides, (d) thio compounds, (e)hexaarylbiimidazole compounds, (f) ketoxime ester compounds, (g) boratecompounds, (h) azinium compounds, (i) metallocene compounds, (j) activeester compounds, (k) compounds having a carbon-halogen bond, and (l)alkylamine compounds. These radical polymerization initiators may beused singly or in a combination of the above-mentioned compounds (a) to(l). The radical polymerization initiators of the present invention aresuitably used singly or in a combination of two or more types.

(H) Other Components

The ink composition of the present invention may comprise othercomponents as necessary. Examples of the other components include basiccompounds, polymerization inhibitors, and solvents.

It is preferable to add the basic compound from the viewpoint ofimproving the storage stability of the ink composition. As the basiccompound that can be used in the present invention, a known basiccompound may be used and, for example, a basic inorganic compound suchas an inorganic salt or a basic organic compound such as an amine ispreferably used.

It is preferable to add the polymerization inhibitor from the viewpointof enhancing the storage stability. When the ink composition of thepresent invention is used as an inkjet recording ink composition, it ispreferably heated in the range of 40° C. to 80° C. to thus make it lessviscous and then discharged, and in order to prevent clogging of a headdue to thermal polymerization it is preferable to add a polymerizationinhibitor. The polymerization inhibitor is preferably added at 200 to20,000 ppm relative to the total amount of the ink composition of thepresent invention. Examples of the polymerization inhibitor includehydroquinone, benzoquinone, p-methoxyphenol, TEMPO, TEMPOL, and AIcupferron.

While taking into consideration the ink composition and the inkjetrecording ink composition of the present invention being radiationcuring type ink compositions, it is preferable for them not to containany solvent so that the ink compositions can react quickly and be curedimmediately after landing. However, as long as the curing speed, etc. ofthe ink composition is not affected, a specified solvent may be added.In the present invention, as a solvent, an organic solvent or water maybe used. In particular, the organic solvent may be added in order toimprove the adhesion to a recording medium (a support such as paper).Adding an organic solvent is effective since the problem with VolatileOrganic Compound (VOC) can be avoided. The amount of organic solvent ispreferably 0.1 to 5 wt % relative to the total amount of the inkcomposition of the present invention, and more preferably 0.1 to 3 wt %.

As means for preventing the sensitivity from being degraded by a lightblocking effect of the colorant, which may be added to the inkcomposition, a combination of a cationically polymerizable compound anda cationic polymerization initiator, a combination of a radicallypolymerizable compound and a radical polymerization initiator, or aradical/cationic hybrid curing ink combining a polymerizable compoundand a polymerization initiator may be employed.

In addition to the above, the ink composition of the present inventionmay contain a known compound as necessary. Examples thereof include asurfactant (cationic, anionic, nonionic, fluorine-based, silicon-based),a leveling additive, a matting agent and, for adjusting film physicalproperties, a polyester resin, polyurethane resin, vinyl resin, acrylicresin, rubber resin, or wax, which may be appropriately selected andadded. Furthermore, in order to improve the adhesion to a recordingmedium such as a polyolefin or PET, a tackifier that does not inhibitpolymerization is preferably added. Specific examples of the tackifierinclude high molecular weight tacky polymers described on pp. 5 and 6 ofJP-A-2001-49200 (e.g. a copolymer formed from an ester of (meth)acrylicacid and an alcohol having an alkyl group with 1 to 20 carbons, an esterof (meth)acrylic acid and an alicyclic alcohol having 3 to 14 carbons,or an ester of (meth)acrylic acid and an aromatic alcohol having 6 to 14carbons), and a low molecular weight tackifying resin having apolymerizable unsaturated bond.

(2) Properties of Ink Composition

The ink composition of the present invention comprises as describedabove (A) a compound represented by any one of Formulae (I) to (XI), (B)a cationically polymerizable compound, and (C) a colorant, etc. Withregard to the content of these components relative to the total weightof the ink composition, the compound (A) represented by any one ofFormulae (I) to (XI) is preferably 0.01 to 20 parts by weight, and morepreferably 0.5 to 10 parts by weight, the cationically polymerizablecompound (B) is preferably 10 to 95 wt %, more preferably 30 to 93 wt %,and yet more preferably 50 to 90 wt %, the colorant (C) is preferably 1to 10 wt %, and more preferably 2 to 8 wt %, and each component iscontained so that the total of the components, expressed as wt %,desirably becomes 100 wt %. Furthermore, needless to say, the inkcomposition of the present invention may comprise any component such asthe sensitizer (D).

When the ink composition thus obtained is used for inkjet recording,while taking into consideration dischargability, the viscosity of theink composition at the discharge temperature (e.g. 25° C. to 80° C., andpreferably 25° C. to 30° C.) is preferably 7 to 30 mPa·s, and morepreferably 7 to 20 mPa·s. For example, the ink composition of thepresent invention has a viscosity at room temperature (25° C. to 30° C.)of preferably 35 to 500 mPa·s, and more preferably 35 to 200 mPa·s. Withregard to the ink composition of the present invention, it is preferablethat its component ratio is appropriately adjusted so that the viscosityis in the above-mentioned range. When the viscosity at room temperatureis set to be high, even when a porous recording medium is used,penetration of the ink into the recording medium can be prevented,uncured monomer can be reduced, and the odor can be reduced.Furthermore, ink spreading when ink droplets have landed can besuppressed, and as a result there is the advantage that the imagequality is improved. When the viscosity at room temperature is set to below, since it is unnecessary to heat the ink when discharging or it ispossible to set the heating temperature at a relatively low temperature,there are the advantages that the load on inkjet equipment becomes smalland the choice of inkjet heads that can be used is widened.

The surface tension of the ink composition of the present invention ispreferably 20 to 30 mN/m, and yet more preferably 23 to 28 mN/m. Whenrecording is carried out on various types of recording medium such aspolyolefin, PET, coated paper, and uncoated paper, from the viewpoint ofspread and penetration, it is preferably at least 20 mN/m, and from theviewpoint of wettability it is preferably not more than 30 mN/m.

(3) Inkjet Recording Method and Equipment

The ink composition of the present invention is preferably used forinkjet recording.

An inkjet recording method that can be suitably employed in the presentinvention is explained below.

(3-1) Inkjet Recording Method

The present invention provides a method for forming an image bydischarging the above-mentioned ink composition onto a recording medium(support, recording material, etc.) and curing the ink composition byirradiating the ink composition so discharged onto the recording mediumwith actinic radiation. That is, the present invention relates to aninkjet recording method comprising:

(A′) a step of discharging an ink composition onto a recording medium;and (B′) a step of curing the ink composition by irradiating the inkcomposition so discharged with actinic radiation,

wherein the ink composition is the ink composition of the presentinvention.

The cured ink composition forms an image on the recording medium.

The peak wavelength of the actinic radiation is preferably 200 to 600nm, more preferably 300 to 450 nm, and yet more preferably 350 to 420nm. The output of the actinic radiation is preferably no greater than2,000 mJ/cm², and is more preferably 10 to 2,000 mJ/cm², yet morepreferably 20 to 1,000 mJ/cm², and particularly preferably 50 to 800mJ/cm².

The inkjet recording method of the present invention is explained bytaking as an example a process for producing a lithographic printingplate, the process comprising discharging an ink composition onto thelithographic printing plate so as to form an image.

A process for producing a lithographic printing plate of the presentinvention comprises:

(A″) a step of discharging the ink composition of the present inventiononto a hydrophilic support, and (B″) a step of irradiating thedischarged ink composition with radiation so as to cure the inkcomposition, thus forming a hydrophobic image on the hydrophilic supportby curing the ink composition. (3-1-1) Hydrophilic Support Used forLithographic Printing Plate

The lithographic printing plate comprises a support and an image formedon the support.

Conventionally, as the lithographic printing plate, a so-called PS platein which an oleophilic photosensitive resin layer is provided on ahydrophilic support has been widely used. In a process for producingthis PS plate, normally, after a mask exposure (surface exposure) iscarried out via a lith film, non-exposed areas are dissolved and removedto give a desired printing plate. However, in recent years, a techniqueof digitizing image information using a computer by electronicallyprocessing, storing, and outputting the information has becomewidespread, and a new image output system that can be used for the abovetechnique has been desired. In particular, a computer to plate (CTP)technique in which a printing plate is directly produced by scanningaccording to digitized image information with highly coherent light suchas laser light without using a lith film has been developed.

As a system for obtaining a lithographic printing plate that makespossible the above scanning exposure, a process for directly producing alithographic printing plate using an ink composition or an inkjetrecording ink composition can be cited. This process involves obtaininga printing plate having a desired image (preferably a hydrophobic image)by discharging an ink onto a support, and preferably a hydrophilicsupport, using an inkjet system, etc., and exposing this to actinicradiation so as to expose an area with the ink composition or the inkjetrecording ink to light. The ink composition or the inkjet recording inksuitable for such a system is the ink composition or the inkjetrecording ink of the present invention.

The support (recording medium) onto which the ink composition or theinkjet recording ink composition of the present invention is dischargedis not particularly limited, and a dimensionally stable sheet-formsupport may be used. The support is preferably a hydrophilic support.The support used in the lithographic printing plate of the presentinvention is not particularly limited, and a dimensionally stablesheet-form support may be used. It is preferable that a material formingthe support has a hydrophilic surface. Examples of materials forming thesupport include paper, paper laminated with a plastic (e.g.polyethylene, polypropylene, polystyrene, etc.), a metal sheet (e.g.aluminum, zinc, copper, etc.), a plastic film (e.g. cellulose diacetate,cellulose triacetate, cellulose propionate, cellulose butyrate,cellulose acetate butyrate, cellulose nitrate, polyethyleneterephthalate, polyethylene, polystyrene, polypropylene, polycarbonate,polyvinyl acetal, etc.), and paper or plastic film on which theabove-mentioned metal is laminated or vapor-deposited. Preferredexamples of the support include a polyester film and aluminum sheet.Among these, aluminum sheet is particularly preferable since thedimensional stability is good and it is relatively inexpensive.

The aluminum sheet is a pure aluminum sheet, an alloy sheet containingaluminum as a main component and a small amount of a different element,or a thin film of aluminum or an aluminum alloy laminated with aplastic. Examples of the different element contained in the aluminumalloy include silicon, iron, manganese, copper, magnesium, chromium,zinc, bismuth, nickel, and titanium. The content of the differentelement in the alloy is preferably equal to or less than 10 wt %. In thepresent invention, a pure aluminum sheet is preferable, but since it isdifficult to produce completely pure aluminum because of the refiningtechnique, a trace amount of a different element may be contained. Thecomposition of the aluminum sheet is not specified, and a knowngenerally used material may be utilized as appropriate.

The support preferably has a thickness of 0.1 to 0.6 mm, and morepreferably 0.15 to 0.4 mm.

Prior to the aluminum sheet being used, it is preferably subjected to asurface treatment such as a surface roughening treatment or an anodizingtreatment. Surface treatment makes it easy to improve the hydrophilicityand ensure that there is good adhesion between an image recording layerand the support. Prior to the aluminum sheet being subjected to thesurface roughening treatment, it may be subjected as desired to adegreasing treatment using a surfactant, an organic solvent, an aqueousalkaline solution, etc. in order to remove rolling oil on the surface.

The surface roughening treatment for the aluminum sheet surface may becarried out by various types of methods, and examples thereof include amechanical surface roughening treatment, an electrochemical surfaceroughening treatment (a surface roughening treatment involvingdissolving the surface electrochemically), and a chemical surfaceroughening treatment (a surface roughening treatment involvingselectively dissolving the surface chemically).

As a method for the mechanical surface roughening treatment, a knownmethod such as a ball grinding method, a brush grinding method, a blastgrinding method, or a buff grinding method may be used. It is alsopossible to use a transfer method in which an irregular shape istransferred using a roller provided with irregularities in an aluminumrolling stage.

As a method for the electrochemical surface roughening treatment, forexample, a method in which alternating current or direct current isapplied in an electrolyte solution containing an acid such ashydrochloric acid or nitric acid can be cited. It is also possible toemploy a method as described in JP-A-54-63902 in which a mixed acid isused.

The aluminum sheet subjected to a surface roughening treatment issubjected as necessary to an alkali etching treatment using an aqueoussolution of potassium hydroxide, sodium hydroxide, etc.; furthermore,after neutralization, it may be subjected to an anodizing treatment asdesired in order to improve the abrasion resistance.

As an electrolyte that may be used for the anodizing treatment of thealuminum sheet, various types of electrolytes that form a porous oxidefilm may be used. In general, sulfuric acid, hydrochloric acid, oxalicacid, chromic acid, or a mixed acid thereof may be used. Theconcentration of the electrolyte may be determined as appropriateaccording to the type of electrolyte.

Conditions for the anodizing treatment depend on the type of electrolyteused and cannot be specified, but in general the electrolyte solutionconcentration is 1 to 80 wt %, the solution temperature is 5° C. to 70°C., the current density is 5 to 60 A/dm², the voltage is 1 to 100V, andthe electrolysis time is 10 sec. to 5 min. The amount of anodized filmformed is preferably 1.0 to 5.0 g/m², and more preferably 1.5 to 4.0g/m². It is preferable for it to be in this range since good plate lifeand good scratch resistance of a non-image area of a lithographicprinting plate can be obtained.

As the support that can be used in the present invention, a substratethat has been subjected to the above-mentioned surface treatment and hasan anodized film may be used as it is, but in order to further improvethe adhesion to an upper layer, and the hydrophilicity, thecontamination resistance, the thermal insulation, etc., the substratemay appropriately be subjected as necessary to a treatment for enlargingmicropores of the anodized film, a sealing treatment, or a surfacehydrophilization treatment involving immersion in an aqueous solutioncontaining a hydrophilic compound, which are described inJP-A-2001-253181 or JP-A-2001-322365. These enlarging and sealingtreatments are not limited to those described therein, and anyconventionally known methods may be employed.

Sealing Treatment

The sealing treatment may be vapor sealing, a treatment with an aqueoussolution containing an inorganic fluorine compound such as a singletreatment with fluorozirconic acid or a treatment with sodium fluoride,vapor sealing with added lithium chloride, or a sealing treatment withhot water.

Among these, the sealing treatment with an aqueous solution containingan inorganic fluorine compound, the sealing treatment with vapor, andthe sealing treatment with hot water are preferable. Each thereof isexplained below.

Sealing Treatment with Aqueous Solution Containing Inorganic FluorineCompound

In the sealing treatment with an aqueous solution containing aninorganic fluorine compound, a metal fluoride can suitably be used asthe inorganic fluorine compound.

Specific examples thereof include sodium fluoride, potassium fluoride,calcium fluoride, magnesium fluoride, sodium fluorozirconate, potassiumfluorozirconate, sodium fluorotitanate, potassium fluorotitanate,ammonium fluorozirconate, ammonium fluorotitanate, potassiumfluorotitanate, fluorozirconic acid, fluorotitanic acid,hexafluorosilicic acid, nickel fluoride, iron fluoride, fluorophosphoricacid, and ammonium fluorophosphate. Among them, sodium fluorozirconate,sodium fluorotitanate, fluorozirconic acid, and fluorotitanic acid arepreferable.

The concentration of the inorganic fluorine compound in the aqueoussolution is preferably at least 0.01 wt % from the viewpoint of sealingof micropores on an anodized coating being carried out sufficiently, andmore preferably at least 0.05 wt %, and it is preferably no greater than1 wt % from the viewpoint of contamination resistance, and morepreferably no greater than 0.5 wt %.

The aqueous solution containing an inorganic fluorine compoundpreferably further contains a phosphate compound. It is preferable for aphosphate compound to be contained since the hydrophilicity of thesurface of the anodized coating improves and the machine developabilityand the contamination resistance can be improved.

Preferred examples of the phosphate compound include phosphates of ametal such as an alkali metal or an alkaline earth metal.

Specific examples thereof include zinc phosphate, aluminum phosphate,ammonium phosphate, ammonium phosphate dibasic, ammonium dihydrogenphosphate, potassium dihydrogen phosphate, potassium phosphate dibasic,calcium phosphate, ammonium sodium hydrogen phosphate, magnesiumhydrogen phosphate, magnesium phosphate, ferrous phosphate, ferricphosphate, sodium dihydrogen phosphate, sodium phosphate, sodiumphosphate dibasic, lead phosphate, calcium dihydrogen phosphate, lithiumphosphate, phosphotungstic acid, ammonium phosphotungstate, sodiumphosphotungstate, ammonium phosphomolybdate, sodium phosphomolybdate,sodium phosphite, sodium tripolyphosphate, and sodium pyrophosphate.Among these, sodium dihydrogen phosphate, sodium phosphate dibasic,potassium dihydrogen phosphate, and potassium phosphate dibasic arepreferable.

The combination of the inorganic fluorine compound and the phosphatecompound is not particularly limited, but the aqueous solutionpreferably comprises at least sodium fluorozirconate as the inorganicfluorine compound and at least sodium dihydrogen phosphate as thephosphate compound.

The concentration of the phosphate compound in the aqueous solution ispreferably at least 0.01 wt % from the viewpoint of improving machinedevelopability and contamination resistance, and more preferably atleast 0.1 wt %, and it is preferably no greater than 20 wt % from theviewpoint of solubility, and more preferably no greater than 5 wt %.

The proportion of each compound in the aqueous solution is notparticularly limited, but the ratio by weight of the inorganic fluorinecompound and the phosphate compound is preferably 1/200 to 10/1, andmore preferably 1/30 to 2/1.

Furthermore, the temperature of the aqueous solution is preferably atleast 20° C., and more preferably at least 40° C., and it is preferablyno higher than 100° C., and more preferably no higher than 80° C.

Moreover, the pH of the aqueous solution is preferably at least 1, andmore preferably at least 2, and it is preferably no greater than 11, andmore preferably no greater than 5.

A method for the sealing treatment with the aqueous solution containingan inorganic fluorine compound is not particularly limited and, forexample, an immersion method and a spray method may be used. They may beemployed once or a plurality of times, or in a combination of two ormore types.

Among these, the immersion method is preferable. When the treatment iscarried out by the immersion method, the treatment time is preferably atleast 1 sec., and more preferably at least 3 sec., and it is preferablyno greater than 100 sec., and more preferably no greater than 20 sec.

Sealing Treatment with Steam

With regard to the sealing treatment with steam, for example, a methodin which an anodized coating is contacted with steam at high pressure ornormal pressure continuously or discontinuously can be cited.

The temperature of the steam is preferably at least 80° C., and morepreferably at least 95° C., and it is preferably no greater than 105° C.

The pressure of the steam is preferably in the range of (atmosphericpressure−50 mmAq) to (atmospheric pressure+300 mmAq) (1.008×10⁵ to1.043×10⁵ Pa).

Furthermore, the time for which the coating is contacted with steam ispreferably at least 1 sec., and more preferably at least 3 sec., and itis preferably no greater than 100 sec., and more preferably no greaterthan 20 sec.

Sealing Treatment with Hot Water

With regard to the sealing treatment with hot water, for example, amethod in which an aluminum plate having an anodized coating formedthereon is immersed in hot water can be cited.

The hot water may contain an inorganic salt (e.g. a phosphate) or anorganic salt.

The temperature of the hot water is preferably at least 80° C., and morepreferably at least 95° C., and it is preferably no greater than 100° C.

Furthermore, the time for which immersion in hot water is carried out ispreferably at least 1 sec., and more preferably at least 3 sec., and itis preferably no greater than 100 sec., and more preferably no greaterthan 20 sec.

With regard to a hydrophilization treatment that is used in the presentinvention, there is an alkali metal silicate method, as disclosed inU.S. Pat. Nos. 2,714,066, 3,181,461, 3,280,734, and 3,902,734. In thismethod, a support is immersed in an aqueous solution of sodium silicate,etc., or subjected to electrolysis. In addition, there is a method inwhich a support is treated with potassium fluorozirconate, as describedin JP-B-36-22063, and a method in which a support is treated withpolyvinylphosphonic acid, as described in U.S. Pat. Nos. 3,276,868,4,153,461, and 4,689,272.

In the present invention, it is preferable for the support to have acenter line average roughness of 0.10 to 1.2 μm. It is preferable for itto be in this range since good adhesion to an image recording layer,good plate life, and good contamination resistance can be obtained.

(3-1-2) Step of Discharging Ink Composition onto Hydrophilic Support

When the ink composition or the inkjet recording ink composition of thepresent invention is discharged onto the surface of the above-mentionedhydrophilic support, the ink composition or the inkjet recording inkcomposition is preferably discharged after being heated to preferably25° C. to 80° C., and more preferably 25° C. to 30° C., so as to reducethe viscosity of the ink composition to preferably 7 to 30 mPa·s, andmore preferably 7 to 20 mPa·s. In particular, it is preferable to usethe ink composition having an ink viscosity at 25° C. of 35 to 500 mPa·ssince a large effect can be obtained. By employing this method, highdischarge stability can be realized. The radiation curing type inkcomposition such as the ink composition of the present inventiongenerally has a viscosity that is higher than that of a normal inkcomposition or a water-based ink used for an inkjet recording ink, andvariation in viscosity due to a change in temperature at the time ofdischarge is large. Viscosity variation in the ink has a large effect onchanges in liquid droplet size and changes in liquid droplet dischargespeed and, consequently, causes the image quality to be degraded. It istherefore necessary to maintain the ink discharge temperature asconstant as possible. In the present invention, the control range forthe temperature is desirably ±5° C. of a set temperature, preferably ±2°C. of the set temperature, and more preferably ±1° C. of the settemperature.

(3-1-3) Step of Curing Ink Composition by Irradiating Discharged InkComposition with Actinic Radiation so as to Form Hydrophobic Image onHydrophilic Support by Curing Ink Composition

The ink composition discharged onto the surface of the hydrophilicsupport is cured by irradiating with actinic radiation. This resultsfrom a sensitizer in a polymerization initiation system contained in theabove-mentioned ink composition of the present invention absorbingactinic radiation, attaining an excited state, and coming into contactwith a polymerization initiator in the polymerization initiation systemto thus decompose the polymerization initiator, and a polymerizablecompound undergoing radical polymerization and being cured.

The actinic radiation used in this process may include α rays, γ rays,an electron beam, X rays, UV rays, visible light, and IR rays. Althoughit depends on the absorption characteristics of the sensitizer, the peakwavelength of the actinic radiation is, for example, 200 to 600 nm,preferably 300 to 450 nm, and more preferably 350 to 450 nm.Furthermore, in the present invention, the polymerization initiationsystem has sufficient sensitivity for low output actinic radiation. Theoutput of the actinic radiation as irradiation energy is preferably2,000 mJ/cm² or less, more preferably 10 to 2,000 mJ/cm², yet morepreferably 20 to 1,000 mJ/cm², and particularly preferably 50 to 800mJ/cm². Moreover, the actinic radiation is applied so that theillumination intensity on the exposed surface is, for example, 10 to2,000 mW/cm², and preferably 20 to 1,000 mW/cm².

The ink composition of the present invention is desirably exposed tosuch actinic radiation for, for example, 0.01 to 120 sec., andpreferably 0.1 to 90 sec.

Irradiation conditions and a basic method for irradiation with actinicradiation are disclosed in JP-A-60-132767. Specifically, a light sourceis provided on either side of a head unit that includes an ink dischargedevice, and the head unit and the light source are made to scan by aso-called shuttle system. Irradiation with actinic radiation is carriedout after a certain time (e.g. 0.01 to 0.5 sec., preferably 0.01 to 0.3sec., and more preferably 0.01 to 0.15 sec.) has elapsed from when theink has landed. By controlling the time from ink landing to irradiationso as to be a minimum in this way, it becomes possible to prevent theink that has landed on a recording medium from spreading before beingcured. Furthermore, since the ink can be exposed before it reaches adeep area of a porous recording medium that the light source cannotreach, it is possible to prevent monomer from remaining unreacted, andas a result the odor can be reduced.

Furthermore, curing may be completed using another light source that isnot driven. WO99/54415 discloses, as an irradiation method, a methodemploying an optical fiber and a method in which a collimated lightsource is incident on a mirror surface provided on a head unit sideface, and a recorded area is irradiated with UV light.

By employing such a recording method, it is possible to maintain auniform dot diameter for landed ink even for various types of recordingmedia having different surface wettability, thereby improving the imagequality. In order to obtain a color image, it is preferable tosuperimpose colors in order from those with a low lightness. Bysuperimposing inks in order from one with low lightness, it is easy forradiation to reach a lower ink, the curing sensitivity is good, theamount of residual monomer decreases, and an improvement in adhesion canbe expected. Furthermore, although it is possible to discharge allcolors and then expose them at the same time, it is preferable to exposeone color at a time from the viewpoint of promoting curing.

In this way, the above-mentioned ink composition of the presentinvention is cured by irradiation with actinic radiation to thus form ahydrophobic image on the surface of the hydrophilic support.

(3-2) Inkjet Recording Device

The inkjet recording device used in the present invention is notparticularly restricted, and a commercial inkjet recording device may beused. That is, in the present invention, recording on a recording mediummay be carried out using a commercial inkjet recording device.

The inkjet recording device that can be used in the present invention isequipped with, for example, an ink supply system, a temperature sensor,and an actinic radiation source.

The ink supply comprises, for example, a main tank containing the inkcomposition of the present invention, a supply pipe, an ink supply tankimmediately before an inkjet head, a filter, and a piezo system inkjethead. The piezo system inkjet head may be driven so as to discharge amultisize dot of preferably 1 to 100 pL, more preferably 8 to 30 pL, ata resolution of preferably 320×320 to 4,000×4,000 dpi, more preferably400×400 to 1,600×1,600 dpi, and yet more preferably 720×720 dpi. Here,dpi referred to in the present invention means the number of dots per2.54 cm.

As described above, since it is desirable for the radiation curing typeink to be discharged at a constant temperature, a section from the inksupply tank to the inkjet head is thermally insulated and heated. Amethod of controlling temperature is not particularly limited, but it ispreferable to provide, for example, temperature sensors at a pluralityof pipe section positions, and control heating according to the ink flowrate and the temperature of the surroundings. The temperature sensorsmay be provided on the ink supply tank and in the vicinity of the inkjethead nozzle. Furthermore, the head unit that is to be heated ispreferably thermally shielded or insulated so that the device main bodyis not influenced by the temperature of the outside air. In order toreduce the printer start-up time required for heating, or in order toreduce the thermal energy loss, it is preferable to thermally insulatethe head unit from other sections and also to reduce the heat capacityof the entire heated unit.

As an actinic radiation source, a mercury lamp, a gas/solid laser, etc.are mainly used, and for UV photocuring inkjet a mercury lamp and ametal halide lamp are widely known. However, from the viewpoint ofprotection of the environment, there has recently been a strong desirefor mercury not to be used, and replacement by a GaN semiconductor UVlight emitting device is very useful from industrial and environmentalviewpoints. Furthermore, LEDs (UV-LED) and LDs (UV-LD) have smalldimensions, long life, high efficiency, and low cost, there is moreoverlittle damage to a substrate by heat generation, and their use as aphotocuring inkjet light source can therefore be expected.

Furthermore, light-emitting diodes (LED) and laser diodes (LD) may beused as a source of actinic radiation. In particular, when a UV raysource is needed, a UV-LED or a UV-LD may be used. For example, NichiaCorporation has marketed a violet LED having a main emission spectrumwavelength of between 365 nm and 420 nm. Furthermore, when a shorterwavelength is needed, U.S. Pat. No. 6,084,250 discloses an LED that canemit actinic radiation whose wavelength is centered between 300 nm and370 nm. Furthermore, another violet LED is available, and irradiationcan be carried out with radiation of a different UV bandwidth. Theactinic radiation source particularly preferable in the presentinvention is a UV-LED, and a UV-LED having a peak wavelength at 350 to420 nm is particularly preferable.

The maximum illumination intensity of the LED on a recording medium ispreferably 10 to 2,000 mW/cm², more preferably 20 to 1,000 mW/cm², andparticularly preferably 50 to 800 mJ/cm².

In accordance with the present invention, it is possible to provide anink composition that cures with high sensitivity when exposed to actinicradiation and has excellent thermal stability, and an inkjet recordingmethod employing the ink composition.

Furthermore, a printed material obtained using the ink compositioncapable of curing with high sensitivity when exposed to actinicradiation and having excellent thermal stability has high image qualityand excellent strength for an image area. Similarly, in accordance withuse of the ink composition of the present invention, there is exhibitedthe effect that a lithographic printing plate having a long plate lifeand high image quality can be produced based on digital data.

EXAMPLES

The present invention is explained in further detail by reference toExamples and Comparative Examples. However, the present invention shouldnot be construed as being limited to these Examples.

Preparation of Pigment Dispersions

Pigment dispersions 1 of each of yellow, magenta, cyan, black, and whitewere prepared according to the method below. Dispersion conditions wereappropriately adjusted using a known dispersing device so that theaverage particle size of the pigment particles in each case was in therange of 0.2 to 0.3 μm, and subsequently they were filtered using afilter while heating.

Yellow pigment dispersion 1 (C) Cl Pigment Yellow 13   20 parts byweight Polymeric dispersant (Solsperse series, manufactured by Zeneca)  20 parts by weight (B) OXT-221 (manufactured by Toagosei Co., Ltd.)  60 parts by weight Magenta pigment dispersion 1 (C) Cl Pigment Red57:1   20 parts by weight Polymeric dispersant (Solsperse series,manufactured by Zeneca)   20 parts by weight (B) OXT-221 (manufacturedby Toagosei Co., Ltd.)   60 parts by weight Cyan pigment dispersion 1(C) Cl Pigment Blue 15:3   20 parts by weight Polymeric dispersant(Solsperse series, manufactured by Zeneca)   20 parts by weight (B)OXT-221 (manufactured by Toagosei Co., Ltd.)   60 parts by weight Blackpigment dispersion 1 (C) Cl Pigment Black 7   20 parts by weightPolymeric dispersant (Solsperse series, manufactured by Zeneca)   20parts by weight (B) OXT-221 (manufactured by Toagosei Co., Ltd.)   60parts by weight White pigment dispersion 1 (C) Titanium oxide (averageparticle size 0.15 μm, 25.00 parts by weight refractive index 2.52)Neutral polymer dispersant PB822 (manufactured by Ajinomoto-   14 partsby weight Fine-Techno Co., Inc.) Fluorescent whitening agent Uvitex-OB 1.00 part by weight (manufactured by Ciba) (B) OXT-221 (manufactured byToagosei Co., Ltd.)   60 parts by weight Preparation of inks Example 1Yellow ink 1 Yellow pigment dispersion 1 (containing (C))    5 parts byweight (A) Acid-generating compound A below    6 parts by weight (D)Sensitizer: 9,10-dibutoxyanthracene    3 parts by weight (B)Polymerizable compounds Monomer:3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexanecarboxylate   40 partsby weight (Celloxide 2021A: manufactured by Daicel-UCB Co., Ltd.)Monomer: 3,7-bis(3-oxetanyl)-5-oxanonane   45 parts by weight (OXT-221:manufactured by Toagosei Co., Ltd.) Surfactant: BYK307 (manufactured byBYK Chemie)    1 part by weight

Acid-generating compound A Magenta ink 1 Magenta pigment dispersion 1(containing (C))    5 parts by weight (A) Acid-generating compound Aabove    6 parts by weight (B) Polymerizable compounds Monomer:3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexanecarboxylate   40 partsby weight (Celloxide 2021A: manufactured by Daicel-UCB Co., Ltd.)Monomer: 3,7-bis(3-oxetanyl)-5-oxanonane   48 parts by weight (OXT-221:manufactured by Toagosei Co., Ltd.) Surfactant: BYK307 (manufactured byBYK Chemie)    1 part by weight Cyan ink 1 Cyan pigment dispersion 1(containing (C))    5 parts by weight (A) Acid-generating compound Aabove    6 parts by weight (B) Polymerizable compounds Monomer:3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexanecarboxylate   40 partsby weight (Celloxide 2021A: manufactured by Daicel-UCB Co., Ltd.)Monomer: 3,7-bis(3-oxetanyl)-5-oxanonane   48 parts by weight (OXT-221:manufactured by Toagosei Co., Ltd.) Surfactant: BYK307 (manufactured byBYK Chemie)    1 part by weight Black ink 1 Black pigment dispersion 1(containing (C))    5 parts by weight (A) Acid-generating compound Aabove    6 parts by weight (B) Polymerizable compounds Monomer:3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexanecarboxylate   40 partsby weight (Celloxide 2021A: manufactured by Daicel-UCB Co., Ltd.)Monomer: 3,7-bis(3-oxetanyl)-5-oxanonane   48 parts by weight (OXT-221:manufactured by Toagosei Co., Ltd.) Surfactant: BYK307 (manufactured byBYK Chemie)    1 part by weight White ink 1 White pigment dispersion 1(containing (C))    5 parts by weight (A) Acid-generating compound Aabove    6 parts by weight (B) Polymerizable compounds Monomer:3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexanecarboxylate   40 partsby weight (Celloxide 2021A: manufactured by Daicel-UCB Co., Ltd.)Monomer: 3,7-bis(3-oxetanyl)-5-oxanonane   48 parts by weight (OXT-221:manufactured by Toagosei Co., Ltd.) Surfactant: BYK307 (manufactured byBYK Chemie)    1 part by weight

Inks 1 of each color prepared above were filtered using a filter havingan absolute filtration accuracy of 2 μm to give Inks 1 of each color.

Inkjet Image Recording

Subsequently, recording was carried out on a recording medium using acommercial inkjet recording device having a piezo system inkjet nozzle.The ink supply system comprised a main tank, a supply pipe, an inksupply tank immediately before an inkjet head, a filter, and a piezosystem inkjet head, and a section from the ink supply tank to the inkjethead was thermally insulated and heated. Temperature sensors wereprovided on the ink supply tank and in the vicinity of the nozzle of theinkjet head, and the temperature was controlled so that the nozzlesection was always at 70° C.±2° C. The piezo system inkjet head wasdriven so as to discharge multisize dots of 8 to 30 pL at a resolutionof 720×720 dpi. The exposure system, the main scanning speed, and thedischarge frequency were adjusted so that, after landing, UV light wasfocused to give an exposure area illumination intensity of 100 mW/cm²,and irradiation started 0.1 sec. after the ink landed on the recordingmedium. Furthermore, the exposure time was made variable, and exposureenergy was applied. Here, dpi referred to in the present inventiondenotes the number of dots per 2.54 cm.

The inks of each color prepared above were discharged at anenvironmental temperature of 25° C. in the orderblack→cyan→magenta→yellow→white, and irradiation with ultraviolet rayswas carried out using a VZero 085 metal halide lamp manufactured byIntegration Technology after each color was discharged. As an energylevel that could completely cure the inks so that tackiness disappearedwhen touched by hand, the total exposure energy per color was 50 mJ/cm²for all the colors. As recording media, a grained aluminum support, atransparent biaxially stretched polypropylene film whose surface hadbeen treated so as to impart printability, a soft vinyl chloride sheet,a cast coat paper, and a commercial recycled paper were used, each colorimage was recorded, and an image having high resolution without dotspreading was obtained in all cases. Furthermore, for high qualitypaper, the ink did not penetrate to the reverse side, the ink wassufficiently cured, and there was hardly any odor of unreacted monomer.Moreover, the ink recorded on the film had sufficient flexibility, theink did not crack when bent, and there was no problem in an adhesiontest involving peeling with Sellotape™.

Examples 2 to 8 and Comparative Examples 1 to 5 Preparation of Ink

Magenta inks 2 to 11 were prepared in accordance with the methodsdescribed below.

Example 2 Magenta Ink 2

Magenta ink 2 was prepared in the same manner as for Magenta ink 1except that Acid-generating compound B below was used instead ofAcid-generating compound A above.

Example 3 Magenta Ink 3

Magenta ink 3 was prepared in the same manner as for Magenta ink 1except that Acid-generating compound C below was used instead ofAcid-generating compound A above.

Example 4 Magenta Ink 4

Magenta ink 4 was prepared in the same manner as for Magenta ink 1except that Acid-generating compound D below was used instead ofAcid-generating compound A above.

Example 5 Magenta Ink 5

Magenta ink 5 was prepared in the same manner as for Magenta ink 1except that Acid-generating compound E below was used instead ofAcid-generating compound A above.

Example 6 Magenta Ink 6

Magenta ink 6 was prepared in the same manner as for Magenta ink 1except that Acid-generating compound F below was used instead ofAcid-generating compound A above.

Example 7 Magenta Ink 7

Magenta ink 7 was prepared in the same manner as for Magenta ink 1except that Acid-generating compound G below was used instead ofAcid-generating compound A above.

Example 8 Magenta Ink 8

Magenta ink 8 was prepared in the same manner as for Magenta ink 1except that Acid-generating compound H below was used instead ofAcid-generating compound A above.

Example 9 Magenta Ink 9

Magenta ink 9 was prepared in the same manner as for Magenta ink 1except that 3 parts by weight of 9,10-dibutoxyanthracene was added toMagenta ink 1.

Example 10 Magenta Ink 10

Magenta pigment dispersion 1 (containing (C))  5 parts by weight (A)Acid-generating compound A above  6 parts by weight (B) Polymerizablecompounds Cationically polymerizable monomer: 30 parts by weight3,4-epoxycyclohexylmethyl-3′,4′- epoxycyclohexanecarboxylate (Celloxide2021A: manufactured by Daicel-UCB Co., Ltd.) Cationically polymerizablemonomer: 48 parts by weight 3,7-bis(3-oxetanyl)-5-oxanonane (OXT-221:manufactured by Toagosei Co., Ltd.) Radically polymerizable monomer:1,6-hexanediol 10 parts by weight diacrylate

Comparative Example 1 Magenta Ink 11

Magenta pigment dispersion 1 (containing (C))  5 parts by weightUVI-6992 (manufactured by The Dow Chemical  6 parts by weight Company)(B) Polymerizable compounds Monomer: 3,4-epoxycyclohexylmethyl-3′,4′- 40parts by weight epoxycyclohexanecarboxylate (Celloxide 2021A:manufactured by Daicel-UCB Co., Ltd.) Monomer:3,7-bis(3-oxetanyl)-5-oxanonane 48 parts by weight (OXT-221:manufactured by Toagosei Co., Ltd.) Surfactant: BYK307 (manufactured byBYK  1 part by weight Chemie)

Comparative Example 2 Magenta Ink 12

Magenta pigment dispersion 1 (containing (C))  5 parts by weightTri-p-tolylsulfonium hexafluorophosphate (manu-  6 parts by weightfactured by Tokyo Chemical Industry Co., Ltd.) (B) Polymerizablecompounds Monomer: 3,4-epoxycyclohexylmethyl-3′,4′- 40 parts by weightepoxycyclohexanecarboxylate (Celloxide 2021A: manufactured by Daicel-UCBCo., Ltd.) Monomer: 3,7-bis(3-oxetanyl)-5-oxanonane 48 parts by weight(OXT-221: manufactured by Toagosei Co., Ltd.) Surfactant: BYK307(manufactured by BYK  1 part by weight Chemie)

Comparative Examples 3 Magenta Ink 13

Magenta ink 13 was prepared in the same manner as for Magenta ink 11except that Irgacure 250 (manufactured by Ciba Specialty Chemicals) wasused instead of the initiator UVI-6992 (manufactured by The Dow ChemicalCompany).

Comparative Example 4 Magenta Ink 14

Magenta ink 14 was prepared in the same manner as for Magenta ink 11except that 3 parts by weight of 9,10-dibutoxyanthracene was added toMagenta ink 11.

Crude magenta inks 2 to 14 prepared as described above were filteredusing a filter having an absolute filtration accuracy of 2 μm to giveMagenta inks 2 to 14.

Example 11

Magenta ink 15 was prepared in the same manner as for magenta ink 1except that instead of CI pigment red 57:1 Compound M-1 below (oxidationpotential +1.37 V) was used as an oil-soluble dye, and filtration wascarried out using a filter having an absolute filtration accuracy of 2μm.

Example 12

Magenta ink 16 was prepared in the same manner as for magenta ink 1except that instead of CI pigment red 57:1 Compound M-2 below (oxidationpotential +0.94 V) was used as an oil-soluble dye, and filtration wascarried out using a filter having an absolute filtration accuracy of 2μm.

Inkjet Image Recording

A magenta image was printed by the same method as described in Example 1using the magenta inks 2 to 16 prepared above.

Example 13

A magenta image was formed using Magenta ink 9 by the same method as inExample 1 except that a UV light-emitting diode (UV-LED) was usedinstead of the VZero 085 metal halide lamp manufactured by IntegrationTechnology.

In this embodiment, an NCCU033 manufactured by Nichia Corporation wasused as the UV-LED. The LED emits UV light at a wavelength of 365 nmfrom 1 chip, and by applying a current of about 500 mA, light of about100 mW is emitted from the chip. A plurality thereof were aligned atintervals of 7 mm to give a power of 0.3 W/cm² on the surface of arecording medium (hereinafter, also called a medium). The time fromlanding to irradiation and the exposure time can be varied by thetransport speed of the medium and the distance between a head and theLED in the transport direction. In this embodiment, irradiation wascarried out about 0.5 sec. after landing.

The exposure energy on the medium was adjustable in the range of 0.01 to15 J/cm² by setting the distance from the medium and the transportspeed.

Comparative Example 5

A magenta image was formed in the same manner as in Example 13 usingMagenta ink 14.

Inkjet Image Evaluation

Subsequently, with regard to each of the images thus formed, thesensitivity required for curing, penetration into commercial recycledpaper, ink spread on a grained aluminum support, adhesion, plate life,and storage stability were evaluated in accordance with the methodsdescribed below.

1. Curing Sensitivity Measurement

High quality paper was superimposed on a printed sample immediatelyafter exposure, they were passed through pressure rollers (50 kg/cm²),transfer of coloring material onto the high quality paper was evaluated,and the exposure energy intensity (mJ/cm²) when transfer did not occurwas defined as the curing sensitivity. The smaller the value, the higherthe sensitivity.

2. Thermal Stability Evaluation

After storing the prepared ink at 75% RH and 60° C. for 3 days, the inkviscosity at the discharge temperature was measured, and an increase inthe ink viscosity was expressed as a viscosity ratio (afterstorage/before storage). When the viscosity was unchanged and the ratiowas close to 1.0, the storage stability was good, and if the ratioexceeded 1.5, clogging might undesirably be caused during discharge.

3. Cured Film Bending Evaluation

A sample printed at the lowest energy that caused no transfer for eachink was stored at 23° C. for 1 day and then bent through 180°, and thepresence or absence of cracks in the cured film was examined andevaluated as follows. The evaluation results are given in Table 2.

Good: no change Fair: small cracks occurred in the bent portion. Poor:cured film peeled off in the bent portion. 4. Solubility Evaluation

An ink comprising the above-mentioned ink composition without thepigment dispersion was conditioned by stirring for 30 minutes andfiltered using a filter having an absolute filtration accuracy of 2 μm;the presence or absence of a precipitate was evaluated as follows, andthe solubility was evaluated.

Good: no precipitate Fair: small amount of precipitate Poor: someprecipitate 5. Evaluation of Adhesion to Grained Aluminum Support

With regard to the printed images formed above, a completely undamagedsample and a sample whose printed surface was crosshatched with 11 cutsin both lengthwise and widthwise directions at intervals of 1 mm inaccordance with JIS K 5400 to give 100 1 mm squares were prepared,Sellotape™ was affixed to the surface of each sample and peeled offquickly at an angle of 90 degrees, and the condition of the remainingprinted image that had not been peeled off was evaluated in accordancewith the criteria below.

Good: printed image was not peeled off at all in the crosshatch test.Fair: the ink was slightly peeled off in the crosshatch test, but unlessthe ink surface was damaged little was peeled off. Poor: easily peeledoff by Sellotape™ under both conditions. 6. Evaluation of Plate Life

An image printed on a grained aluminum support prepared above was usedas a printing plate, printing was carried out using a Heidel KOR-Dmachine, and a relative comparison of the number of prints completed wasused as an index for the plate life (the number obtained for Example 1was defined as 100). The larger the number, the longer the plate life,which is preferable.

Evaluation results for magenta images formed in Examples 1 to 13 andComparative Examples 1 to 5 are given in Table 2 below.

TABLE 2 Curing sensitivity Thermal Solu- Adhe- Plate Example Ink No.(mJ/cm²) stability bility sion life Ex. 1 Magenta 1 50 1.1 Good Good 100Ex. 2 Magenta 2 40 1.1 Good Good 120 Ex. 3 Magenta 3 40 1.1 Good Good120 Ex. 4 Magenta 4 60 1.1 Good Good 90 Ex. 5 Magenta 5 40 1.1 Good Good120 Ex. 6 Magenta 6 40 1.1 Good Good 120 Ex. 7 Magenta 7 40 1.3 GoodGood 120 Ex. 8 Magenta 8 60 1.3 Good Good 90 Ex. 9 Magenta 9 30 1.2 GoodGood 150 Ex. 10 Magenta 10 30 1.2 Good Good 150 Ex. 11 Magenta 15 40 1.2Good Good 120 Ex. 12 Magenta 16 30 1.2 Good Good 150 Ex. 13 Magenta 9 301.2 Good Good 150 Comp. Ex. 1 Magenta 11 100 1.3 Fair Fair 50 Comp. Ex.2 Magenta 12 120 1.3 Poor Fair 40 Comp. Ex. 3 Magenta 13 80 1.5 FairFair 70 Comp. Ex. 4 Magenta 14 80 1.5 Fair Fair 70 Comp. Ex. 5 Magenta14 80 1.5 Fair Fair 70

It can be seen from Table 2 that the ink composition of the presentinvention that comprises an acid-generating compound having an anionrepresented by Formula (I) or (II), (B) a cationically polymerizablecompound, and (C) a colorant is highly sensitive to irradiation withradiation and has good thermal stability.

With regard to the onium compounds, the starting materials below wereconverted to anions using a base (ref. a method described in Sold StateIonics, 60, (1993), 87-92, etc.), and then subjected to salt exchange(ref. a method described in JP-A-2004-315430, etc.), thus giving varioustypes of onium salt.

Manufactured by Azmax Co., Ltd.

Manufactured by Tokyo Chemical Industry Co., Ltd.

Manufactured by Wako Pure Chemical Industries, Ltd.

Manufactured by Fluka Chemie GmbH

Manufactured by Kanto Chemical Co., Inc. Preparation of PigmentDispersions

Pigment dispersions 2 of each of yellow, magenta, cyan, black, and whitewere prepared according to the method below. Dispersion conditions wereappropriately adjusted using a known dispersing device so that theaverage particle size of the pigment particles in each case was in therange of 0.2 to 0.3 μm, and subsequently they were filtered using afilter while heating.

Yellow pigment dispersion 2 (C) Cl Pigment Yellow 13   20 parts byweight Polymeric dispersant (Solsperse series, manufactured by Zeneca)  20 parts by weight (B) OXT-221 (manufactured by Toagosei Co., Ltd.)  60 parts by weight Magenta pigment dispersion 2 (C) Cl Pigment Red57:1   20 parts by weight Polymeric dispersant (Solsperse series,manufactured by Zeneca)   20 parts by weight (B) OXT-221 (manufacturedby Toagosei Co., Ltd.)   60 parts by weight Cyan pigment dispersion 2(C) Cl Pigment Blue 15:3   20 parts by weight Polymeric dispersant(Solsperse series, manufactured by Zeneca)   20 parts by weight (B)OXT-221 (manufactured by Toagosei Co., Ltd.)   60 parts by weight Blackpigment dispersion 2 (C) Cl Pigment Black 7   20 parts by weightPolymeric dispersant (Solsperse series, manufactured by Zeneca)   20parts by weight (B) OXT-221 (manufactured by Toagosei Co., Ltd.)   60parts by weight White pigment dispersion 2 (C) Titanium oxide (averageparticle size 0.15 μm, 25.00 parts by weight refractive index 2.52)Neutral polymer dispersant PB822 (manufactured by Ajinomoto-   14 partsby weight Fine-Techno Co., Inc.) (B) OXT-221 (manufactured by ToagoseiCo., Ltd.)   60 parts by weight Preparation of inks Example 14 Yellowink 2 Yellow pigment dispersion 2    5 parts by weight (A)Acid-generating compound I below    6 parts by weight (D) Sensitizingcolorant: 9,10-dibutoxyanthracene    3 parts by weight (B) Polymerizablecompounds Monomer:3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexanecarboxylate   40 partsby weight (Celloxide 2021A: manufactured by Daicel-UCB Co., Ltd.)Monomer: 3,7-bis(3-oxetanyl)-5-oxanonane   45 parts by weight (OXT-221:manufactured by Toagosei Co., Ltd.) Surfactant: BYK307 (manufactured byBYK Chemie)    1 part by weight

Acid-generating compound I Magenta ink 17 Magenta pigment dispersion 2   5 parts by weight (A) Acid-generating compound I above    6 parts byweight (B) Polymerizable compounds Monomer:3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexanecarboxylate   40 partsby weight (Celloxide 2021A: manufactured by Daicel-UCB Co., Ltd.)Monomer: 3,7-bis(3-oxetanyl)-5-oxanonane   48 parts by weight (OXT-221:manufactured by Toagosei Co., Ltd.) Surfactant: BYK307 (manufactured byBYK Chemie)    1 part by weight Cyan ink 2 Cyan pigment dispersion 2   5 parts by weight (A) Acid-generating compound I above    6 parts byweight (B) Polymerizable compounds Monomer:3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexanecarboxylate   40 partsby weight (Celloxide 2021A: manufactured by Daicel-UCB Co., Ltd.)Monomer: 3,7-bis(3-oxetanyl)-5-oxanonane   48 parts by weight (OXT-221:manufactured by Toagosei Co., Ltd.) Surfactant: BYK307 (manufactured byBYK Chemie)    1 part by weight Black ink 2 Black pigment dispersion 2   5 parts by weight (A) Acid-generating compound I above    6 parts byweight (B) Polymerizable compounds Monomer:3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexanecarboxylate   40 partsby weight (Celloxide 2021A: manufactured by Daicel-UCB Co., Ltd.)Monomer: 3,7-bis(3-oxetanyl)-5-oxanonane   48 parts by weight (OXT-221:manufactured by Toagosei Co., Ltd.) Surfactant: BYK307 (manufactured byBYK Chemie)    1 part by weight White ink 2 White pigment dispersion 2   5 parts by weight (A) Acid-generating compound I above    6 parts byweight (B) Polymerizable compounds Monomer:3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexanecarboxylate   40 partsby weight (Celloxide 2021A: manufactured by Daicel-UCB Co., Ltd.)Monomer: 3,7-bis(3-oxetanyl)-5-oxanonane   48 parts by weight (OXT-221:manufactured by Toagosei Co., Ltd.) Surfactant: BYK307 (manufactured byBYK Chemie)    1 part by weight

Yellow ink 2, Magenta ink 17, Cyan ink 2, Black ink 2, and White ink 2prepared above were filtered using a filter having an absolutefiltration accuracy of 2 μm to give Inks of each color.

Inkjet Image Recording

Subsequently, recording was carried out on a recording medium using acommercial inkjet recording device having a piezo system inkjet nozzle.The ink supply system comprised a main tank, a supply pipe, an inksupply tank immediately before an inkjet head, a filter, and a piezosystem inkjet head, and a section from the ink supply tank to the inkjethead was thermally insulated and heated. Temperature sensors wereprovided on the ink supply tank and in the vicinity of the nozzle of theinkjet head, and the temperature was controlled so that the nozzlesection was always at 70° C.±2° C. The piezo system inkjet head wasdriven so as to discharge multisize dots of 8 to 30 pL at a resolutionof 720×720 dpi. The exposure system, the main scanning speed, and thedischarge frequency were adjusted so that, after landing, UV light wasfocused to give an exposure area illumination intensity of 100 mW/cm²,and irradiation started 0.1 sec. after the ink landed on the recordingmedium. Furthermore, the exposure time was made variable, and exposureenergy was applied. Here, dpi referred to in the present inventiondenotes the number of dots per 2.54 cm.

The inks of each color prepared above were discharged at anenvironmental temperature of 25° C. in the orderblack→cyan→magenta→yellow→white, and irradiation with ultraviolet rayswas carried out using a VZero 085 metal halide lamp, manufactured byIntegration Technology after each color was discharged. As an energylevel that could completely cure the inks so that tackiness disappearedwhen touched by hand, the total exposure energy per color was 200 mJ/cm²for all the colors. As recording media, a grained aluminum support, atransparent biaxially stretched polypropylene film whose surface hadbeen treated so as to impart printability, a soft vinyl chloride sheet,a cast coat paper, and a commercial recycled paper were used, each colorimage was recorded, and an image having high resolution without dotspreading was obtained in all cases. Furthermore, for high qualitypaper, the ink did not penetrate to the reverse side, the ink wassufficiently cured, and there was hardly any odor of unreacted monomer.Moreover, the ink recorded on the film had sufficient flexibility, theink did not crack when bent, and there was no problem in an adhesiontest involving peeling with Sellotape™.

Examples 15 to 26 and Comparative Examples 6 to 10 Preparation of Ink

Magenta inks 18 to 32 were prepared in accordance with the methoddescribed below.

Example 15 Magenta Ink 18

Magenta ink 18 was prepared in the same manner as for Magenta ink 17except that Acid-generating compound J below was used instead ofAcid-generating compound I above.

Example 16 Magenta Ink 19

Magenta ink 19 was prepared in the same manner as for Magenta ink 17except that Acid-generating compound K below was used instead ofAcid-generating compound I above.

Example 17 Magenta Ink 20

Magenta ink 20 was prepared in the same manner as for Magenta ink 17except that Acid-generating compound L below was used instead ofAcid-generating compound I above.

Example 18 Magenta Ink 21

Magenta ink 21 was prepared in the same manner as for Magenta ink 17except that Acid-generating compound M below was used instead ofAcid-generating compound I above.

Example 19 Magenta Ink 22

Magenta ink 22 was prepared in the same manner as for Magenta ink 17except that Acid-generating compound N below was used instead ofAcid-generating compound I above.

Example 20 Magenta Ink 23

Magenta ink 23 was prepared in the same manner as for Magenta ink 17except that Acid-generating compound O below was used instead ofAcid-generating compound I above.

Example 21 Magenta Ink 24

Magenta ink 24 was prepared in the same manner as for Magenta ink 17except that Acid-generating compound P below was used instead ofAcid-generating compound I above.

Example 22 Magenta Ink 25

Magenta ink 22 was prepared in the same manner as for Magenta ink 17except that 3 parts by weight of 9,10-dibutoxyanthracene was added toMagenta ink 17.

Example 23 Magenta Ink 26

Magenta pigment dispersion 2  5 parts by weight (A) Acid-generatingcompound I above  6 parts by weight (B) Polymerizable compoundsCationically polymerizable monomer: 30 parts by weight3,4-epoxycyclohexylmethyl-3′,4′- epoxycyclohexanecarboxylate (Celloxide2021A: manufactured by Daicel-UCB Co., Ltd.) Cationically polymerizablemonomer: 48 parts by weight 3,7-bis(3-oxetanyl)-5-oxanonane (OXT-221:manufactured by Toagosei Co., Ltd.) Radically polymerizable monomer:1,6-hexanediol 10 parts by weight diacrylate

Comparative Example 6 Magenta Ink 27

Magenta pigment dispersion 2  5 parts by weight Triarylsulfoniumtetrafluoroborate (manufactured  6 parts by weight by Tokyo ChemicalIndustry Co., Ltd.) (B) Polymerizable compounds Monomer:3,4-epoxycyclohexylmethyl-3′, 40 parts by weight4′-epoxycyclohexanecarboxylate (Celloxide 2021A: manufactured byDaicel-UCB Co., Ltd.) Monomer: 3,7-bis(3-oxetanyl)-5-oxanonane 48 partsby weight (OXT-221: manufactured by Toagosei Co., Ltd.) Surfactant:BYK307 (manufactured by BYK  1 part by weight Chemie)

Comparative Example 7 Magenta Ink 28

Magenta pigment dispersion 2  5 parts by weight Tri-p-tolylsulfoniumtrifluoromethanesulfonate  6 parts by weight (manufactured by TokyoChemical Industry Co., Ltd.) (B) Polymerizable compounds Monomer:3,4-epoxycyclohexylmethyl-3′, 40 parts by weight4′-epoxycyclohexanecarboxylate (Celloxide 2021A: manufactured byDaicel-UCB Co., Ltd.) Monomer: 3,7-bis(3-oxetanyl)-5-oxanonane 48 partsby weight (OXT-221: manufactured by Toagosei Co., Ltd.) Surfactant:BYK307 (manufactured by BYK  1 part by weight Chemie)

Comparative Example 29

Magenta pigment dispersion 2  5 parts by weight Tri-p-tolylsulfoniumhexafluorophosphate (manu-  6 parts by weight factured by Tokyo ChemicalIndustry Co., Ltd.) (B) Polymerizable compounds Monomer:3,4-epoxycyclohexylmethyl-3′, 40 parts by weight4′-epoxycyclohexanecarboxylate (Celloxide 2021A: manufactured byDaicel-UCB Co., Ltd.) Monomer: 3,7-bis(3-oxetanyl)-5-oxanonane 48 partsby weight (OXT-221: manufactured by Toagosei Co., Ltd.) Surfactant:BYK307 (manufactured by BYK  1 part by weight Chemie)

Comparative Example 9 Magenta Ink 30

Magenta ink 30 was prepared in the same manner as for Magenta ink 27except that 3 parts by weight of 9,10-dibutoxyanthracene was added toMagenta ink 27.

Crude magenta inks 18 to 30 prepared as described above were filteredusing a filter having an absolute filtration accuracy of 2 μm to giveMagenta inks 18 to 30.

Example 24 Magenta Ink 31

Magenta ink 31 was prepared in the same manner as for magenta ink 17except that instead of CI pigment red 57:1 Compound M-1 below (oxidationpotential +1.37 V) was used as an oil-soluble dye, and filtration wascarried out using a filter having an absolute filtration accuracy of 2μm.

Example 25 Magenta Ink 32

Magenta ink 32 was prepared in the same manner as for magenta ink 17except that instead of CI pigment red 57:1 Compound M-2 below (oxidationpotential +0.94 V) was used as an oil-soluble dye, and filtration wascarried out using a filter having an absolute filtration accuracy of 2μm.

Inkjet Image Recording

A magenta image was printed by the same method as described in Example14 using the magenta inks 18 to 32 prepared above.

Example 26

A magenta image was formed using Magenta ink 25 by the same method as inExample 14 except that a UV light-emitting diode (UV-LED) was usedinstead of the VZero 085 metal halide lamp manufactured by IntegrationTechnology.

In this embodiment, an NCCU033 manufactured by Nichia Corporation wasused as the UV-LED. The LED emits UV light at a wavelength of 365 nmfrom 1 chip, and by applying a current of about 500 mA, light of about100 mW is emitted from the chip. A plurality thereof were aligned atintervals of 7 mm to give a power of 0.3 W/cm² on the surface of arecording medium (hereinafter, also called a medium). The time fromlanding to irradiation and the exposure time can be varied by thetransport speed of the medium and the distance between a head and theLED in the transport direction. In this embodiment, irradiation wascarried out about 0.5 sec. after landing.

The exposure energy on the medium was adjustable in the range of 0.01 to15 J/cm² by setting the distance from the medium and the transportspeed.

Comparative Example 10

A magenta image was formed in the same manner as in Example 26 usingMagenta ink 30.

Inkjet Image Evaluation

Subsequently, with regard to each of the images thus formed, thesensitivity required for curing, penetration into commercial recycledpaper, ink spread on a grained aluminum support, adhesion, plate life,and storage stability were evaluated in accordance with the methodsdescribed below.

1. Curing Sensitivity Measurement

High quality paper was superimposed on a printed sample immediatelyafter exposure, they were passed through pressure rollers (50 kg/cm²),transfer of coloring material onto the high quality paper was evaluated,and the exposure energy intensity (mJ/cm²) when transfer did not occurwas defined as the curing sensitivity. The smaller the value, the higherthe sensitivity.

2. Thermal Stability Evaluation

After storing the prepared ink at 75% RH and 60° C. for 3 days, the inkviscosity at the discharge temperature was measured, and an increase inthe ink viscosity was expressed as a viscosity ratio (afterstorage/before storage). When the viscosity was unchanged and the ratiowas close to 1.0, the storage stability was good, and if the ratioexceeded 1.5, clogging might undesirably be caused during discharge.

3. Solubility Evaluation

An ink comprising the above-mentioned ink composition without thepigment dispersion was conditioned by stirring for 30 minutes andfiltered using a filter having an absolute filtration accuracy of 2 μm;the presence or absence of a precipitate was evaluated as follows, andthe solubility was evaluated.

Good: no precipitate Fair: small amount of precipitate Poor: someprecipitate 4. Evaluation of Adhesion to Grained Aluminum Support

With regard to the printed images formed above, a completely undamagedsample and a sample whose printed surface was crosshatched with 11 cutsin both lengthwise and widthwise directions at intervals of 1 mm inaccordance with JIS K 5400 to give 100 1 mm squares were prepared,Sellotape™ was affixed to the surface of each sample and peeled offquickly at an angle of 90 degrees, and the condition of the remainingprinted image that had not been peeled off was evaluated in accordancewith the criteria below.

Good: printed image was not peeled off at all in the crosshatch test.Fair: the ink was slightly peeled off in the crosshatch test, but unlessthe ink surface was damaged little was peeled off. Poor: easily peeledoff by Sellotape™ under both conditions. 5. Evaluation of Plate Life

An image printed on a grained aluminum support prepared above was usedas a printing plate, printing was carried out using a Heidel KOR-Dmachine, and a relative comparison of the number of prints completed wasused as an index for the plate life (the number obtained for Example 14was defined as 100). The larger the number, the longer the plate life,which is preferable.

TABLE 3 Curing sensitivity Thermal Solu- Adhe- Plate Example Ink No.(mJ/cm²) stability bility sion life Ex. 14 Magenta 17 200 1.1 Good Good100 Ex. 15 Magenta 18 150 1.1 Good Good 120 Ex. 16 Magenta 19 300 1.1Good Good 80 Ex. 17 Magenta 20 300 1.1 Good Good 80 Ex. 18 Magenta 21250 1.1 Good Good 90 Ex. 19 Magenta 22 300 1.1 Good Good 80 Ex. 20Magenta 23 150 1.3 Good Good 120 Ex. 21 Magenta 24 220 1.3 Good Good 95Ex. 22 Magenta 25 100 1.2 Good Good 150 Ex. 23 Magenta 26 150 1.2 GoodGood 120 Ex. 24 Magenta 31 180 1.1 Good Good 110 Ex. 25 Magenta 32 1501.1 Good Good 120 Ex. 26 Magenta 25 100 1.2 Good Good 150 Comp. Ex. 6Magenta 27 500 1.3 Poor Fair 50 Comp. Ex. 7 Magenta 28 1000 1.3 GoodFair 20 Comp. Ex. 8 Magenta 29 400 1.5 Fair Fair 60 Comp. Ex. 9 Magenta30 200 1.3 Poor Fair 100 Comp. Magenta 30 400 1.5 Fair Fair 60 Ex. 10

It can be seen from Table 3 that the ink composition of the presentinvention that comprises an acid-generating compound having an anionrepresented by any one of Formulae (III) to (XI), (B) a cationicallypolymerizable compound, and (C) a colorant is highly sensitive toirradiation with radiation and has good thermal stability and excellentadhesion and plate life.

1. An ink composition comprising: (A) an acid-generating compound having an anion represented by any one of Formulae (I) to (XI); (B) a cationically polymerizable compound; and (C) a colorant,

wherein R¹ to R³ independently denote a monovalent organic group, Rb¹ to Rb³, Rf¹, and Rf² independently denote a perfluoroalkyl group, a perfluoroaryl group, or an aryl group substituted with at least one fluorine atom or perfluoroalkyl group, X¹ to X³ independently denote a monovalent organic group, and Y¹ denotes a hydrogen atom or a monovalent organic group.
 2. The ink composition according to claim 1, wherein the acid-generating compound has an anion represented by either Formula (I) or (II).
 3. The ink composition according to claim 2, wherein the acid-generating compound has any one of the anions below.


4. The ink composition according to claim 1, wherein the acid-generating compound has an anion represented by any one of Formulae (III) to (XI).
 5. The ink composition according to claim 4, wherein the acid-generating compound has any one of the anions below.


6. The ink composition according to claim 4, wherein the acid-generating compound has an anion represented by either Formula (VI) or (X).
 7. The ink composition according to claim 1, wherein the acid-generating compound has an onium ion or an organometallic cation.
 8. The ink composition according to claim 1, wherein the acid-generating compound is a triarylsulfonium salt having an anion represented by any one of Formulae (I) to (XI).
 9. The ink composition according to claim 1, wherein the acid-generating compound is a triarylsulfonium salt substituted with at least one of a fluoro group (—F), a trifluoromethyl group (—CF₃), a chloro group (—Cl), and a bromo group (—Br).
 10. The ink composition according to claim 1, wherein the cationically polymerizable compound comprises a compound having an epoxy group and a compound having an oxetanyl group.
 11. The ink composition according to claim 1, wherein it comprises (D) a sensitizer.
 12. The ink composition according to claim 11, wherein the sensitizer has any one of the skeletons below.


13. The ink composition according to claim 1, wherein it is for inkjet recording use.
 14. An inkjet recording method comprising: a step (A′) of discharging an ink composition onto a recording medium; and a step (B′) of irradiating the discharged ink composition with actinic radiation so as to cure the ink composition, the ink composition being the ink composition according to claim
 1. 15. The inkjet recording method according to claim 14, wherein the actinic radiation is ultraviolet radiation emitted by a light emitting diode that has a light emission peak wavelength in the range of 350 to 420 nm and generates ultraviolet radiation whose maximum illumination intensity on the surface of a recording medium is 10 to 2,000 mW/cm².
 16. A printed material recorded by the inkjet recording method according to claim
 14. 17. A process for producing a lithographic printing plate, the process comprising: a step (A″) of discharging the ink composition according to claim 1 onto a hydrophilic support; and a step (B″) of irradiating the discharged ink composition with actinic radiation so as to cure the ink composition, thus forming a hydrophobic image on the hydrophilic support by curing the ink composition.
 18. A lithographic printing plate produced by the process for producing a lithographic printing plate according to claim
 17. 